delivered the Opinion of the Court.
This is an appeal of a judgment of the Denver Juvenile Court denying a natural father’s motion to set aside a stepparent adoption of his son by the husband of the child’s mother.1 The appellant sought to set aside this stepparent adoption on the basis that his consent authorizing the adoption of his child was invalid because it was induced by an unenforceable promise that he could continue to have visitation rights with respect to his child. The juvenile court declined to set aside the adoption, ruling that appellant’s consent to the adoption of his child was knowingly, intelligently, and voluntarily given. We affirm the judgment of the juvenile court.
I.
Appellant D.J.T. began living with T.O. in 1980 and lived with her for about five years. The two were unmarried during their entire relationship. On June 13, 1983, T.O. gave birth to a son, E.E.F., who is the subject of this dispute. T.O. conceded in an affidavit filed in the subsequent adoption action that D.J.T. was E.E.F.’s natural father.2 Following E.E.F.’s birth, D.J.T. and T.O. continued to live together with their son for about two and one-half years. During that period, D.J.T. exercised at least some of the duties and responsibilities *256of a father, although the exact extent to which he did so was disputed by the parties. In the Fall of 1985, T.O. ended her relationship with D.J.T. and, together with E.E.F., ceased to live with him. On October 18, 1985, T.O. married S.O., the appel-lee stepfather. Following T.O.’s marriage to S.O., D.J.T. continued to maintain a relationship with E.E.F., visiting him periodically in T.O. and S.O.’s home. D.J.T. did not contribute significantly to the costs of E.E.F.’s support, and was not asked to do so by T.O.3
In the Fall of 1986, T.O. approached D.J.T. to discuss the possibility that her husband- S.O. adopt E.E.F. Among other reasons, according to D.J.T., T.O. and S.O. believed it would be better for the child to have S.O.’s last name and be eligible for his medical coverage.4 The evidence presented at the juvenile court hearing on the appellant’s motion to set aside the adoption indicated that the parties understood that D.J.T. would continue to visit E.E.F. after the adoption. The parties dispute, however, whether such visitation was to be as a matter of right for D.J.T. or only so long as T.O. and S.O. consented to such visits. It is undisputed that when T.O. and S.O. obtained a consent form from the juvenile court, they and D.J.T. brought the form to the office of the clerk of the court and asked a clerk whether they could modify the consent form to include a provision recognizing D.J.T.’s right to visit E.E.F. The clerk indicated “there wasn’t any way to change the, wording.” D.J.T. signed the unaltered form.
On October 23, 1986, T.O. and S.O. filed a Petition for Adoption of a Child in Denver Juvenile Court. Included with the petition were D.J.T.’s and T.O.’s separate consents to the adoption. D.J.T.’s consent included a provision under which D.J.T. waived his right to notice of the adoption hearing. D.J.T. received no formal notice of the hearing and D.J.T. testified without contradiction that he was not otherwise informed of the date and time of the hearing. On November 24, 1986, the juvenile court commissioner conducted a hearing on the stepfather’s petition to adopt E.E.F., which D.J.T. did not attend. T.O. and S.O. appeared at the hearing without counsel and were questioned by the commissioner on whether they obtained the consent of the child’s natural father. They assured the court that the father understood that the adoption decree would terminate his relationship with E.E.F. The commissioner determined that E.E.F. was available for adoption and that it “would serve the best interests of all of the parties” to enter an immediate final decree of adoption.
Following the adoption, D.J.T. continued to visit E.E.F. although over time T.O. became increasingly reluctant to permit the visits. Finally, in May of 1987, the appel-lees ceased permitting D.J.T. to visit the child and in August of 1987, they obtained a permanent injunction forbidding D.J.T. from contacting E.E.F.5 About one month after the appellees ceased permitting D.J.T. to visit E.E.F., D.J.T. contacted an attorney and petitioned the juvenile court for a good cause hearing to obtain access to the adoption file. On January 28, 1988, D.J.T. filed in juvenile court what was designated a “Verified Motion to Set Aside Adoption Decree.” On October 20, 1988, the court held a hearing on D.J.T.’s motion, receiving testimony from D.J.T., S.O. and T.O., and reviewed the file in the prior adoption action. The court denied the motion to set aside the adoption decree, finding that the father’s consent to the adoption was “knowingly and intelligently and voluntarily executed.” D.J.T. appealed that decision to the court of appeals, and this case was transferred to this court pursuant to section 13-4-110(l)(a), 6A C.R.S. (1987) be*257cause D.J.T. raised certain questions regarding the constitutionality of the relevant statutes governing stepparent adoptions.
D.J.T. argues that section 19-5-203(l)(f), 8B C.R.S. (1989 Supp.),6 violates principles of due process by permitting the adoption of a child, born out of wedlock, by a stepparent with the consent of only one of the parents and does not provide the other parent with notice or opportunity to be heard, regardless of the child’s substantial relationship with the other parent. D.J.T. argues that this section also violates principles of equal protection because a stepparent adoption of a child whose parents were married but then divorced is permitted only with the consent of both parents. § 19-5-203(l)(e), 8B C.R.S. (1989 Supp.). Finally, D.J.T. argues that even if these statutes are interpreted to avoid constitutional difficulty by requiring consent, notice, and an opportunity to be heard prior to the termination of the parental rights of an unwed parent, the adoption of E.E.F. must be set aside because S.O. and T.O. did not obtain his valid consent and because he received no notice of the adoption hearing. While conceding that he signed a form consenting to the adoption, D.J.T. argues that his consent was given under a mutual mistake of law and fact, namely that it could be conditioned on his continued right to visit E.E.F.
We find that under our statutory scheme, as applied to these facts, the adoption of E.E.F. could not proceed without the consent of his natural father. However, we hold that the juvenile court properly found that D.J.T. validly consented to the adoption. Further, we hold that, although D.J.T. was entitled to notice of the adoption hearing and an opportunity to be heard, D.J.T. waived this right.
II.
Before specifically addressing DJ.T.’s arguments, it is useful to review the statutory scheme governing stepparent adoptions. In E.R.S. v. O.D.A., 779 P.2d 844 (Colo.1989), and in In re Petition of R.H.N., 710 P.2d 482 (Colo.1985), we considered the procedures which the legislature established for the adoption of a child by a stepparent. Adoption in Colorado is a creature of statutory law and is governed by the provisions set out in sections 19-5-201 to -215, 8B C.R.S. (1989 Supp.). The adoption of a child by a stepparent necessarily terminates the parental rights of the noncustodial parent. E.R.S., 779 P.2d at 847; R.H.N., 710 P.2d at 485. To commence a proceeding for a stepparent adoption, the stepparent files an adoption petition pursuant to section 19-5-208, 8B C.R.S. (1989 Supp.). Id. The court must decide whether the child is “available for adoption” pursuant to section 19-5-203, 8B C.R.S. (1989 Supp.). Subsection (1) of that section provides in relevant part:
(1) A child may be available for adoption only upon:
(a) Order of the court terminating the parent-child legal relationship in a proceeding brought under article 3 or 5 of this title;
(b) Order of the court decreeing the voluntary relinquishment of the parent-child legal relationship under section 19-5-103 or 19-5-105;
(c) Written and verified consent of the guardian of the person, appointed by the court, of a child whose parents are deceased;
(d)(1) Written and verified consent of the parent in a stepparent adoption where the other parent is deceased or his parent-child legal relationship has been terminated under paragraph (a) or (b) of this subsection (1);
(II) Written and verified consent of the parent in a stepparent adoption where the other parent has abandoned the child *258for a period of one year or more or where he has failed without cause to provide reasonable support for such child for a period of one year or more. Upon filing of the petition in adoption, the court shall issue a notice directed to the other parent, which notice shall state the nature of the relief sought, the names of the petitioner and the child, and the time and place set for hearing on the petition. If the address of the other parent is known, service of such notice shall be in the manner provided by the Colorado rules of civil procedure for service of process. Upon affidavit by the petitioner that, after diligent search, the address of the other parent remains unknown, the court shall order service upon the other parent by one publication of the notice in a newspaper of general circulation in the county in which the hearing is to be held. The hearing shall not be held sooner than thirty days after service of the notice is complete, and, at such time, the court may enter a final decree of adoption notwithstanding the time limitation in section 19-5-210(2).
(e) Written and verified consent of the parent having only residual parental rights and responsibilities when custody has been awarded to the other parent in a dissolution of marriage proceeding where the spouse of the parent having custody wishes to adopt the child;
(f) Written and verified consent of the parent or parents as defined in section 19-1-103(21) in a stepparent adoption where the child is conceived and born out of wedlock[.]
Here, there was no independent proceeding terminating D.J.T.’s parental rights. Further, unlike E.R.S. or R.H.N., the adoption proceeding did not go forward on the basis that D.J.T. had abandoned E.E.F. but rather on the basis that D.J.T. had consented to E.E.F.’s adoption. Thus, the propriety of E.E.F.’s adoption must be considered under section 19 — 5—203(l)(f), the only subsection by its terms applying to the circumstances of the present case.
Because the statute provides that a child conceived and born out of wedlock is available for adoption with the written and verified consent of the parent or parents,7 D.J.T. argues that this section unconstitutionally permits the adoption of the child of unwed parents with the consent of only one of the parents. However, we reject D.J. T.’s interpretation of section 19 — 5—203(l)(f), and hold that the adoption of E.E.F. was only proper with the valid consent of D.J.T. Thus, we need not address D.J.T.’s constitutional arguments.8
In interpreting a statute, we seek to discern the intent of the legislature. People v. Guenther, 740 P.2d 971 (Colo.1987). We presume that the legislature intends a just and reasonable result when it enacts a statute and we seek to avoid an interpretation leading to an absurd result. Ingram v. Cooper, 698 P.2d 1314 (Colo.1985). We must choose a construction of the statute which best effectuates the purposes of the legislative scheme. Smith v. Myron Stratton Home, 676 P.2d 1196 (Colo.1984). If possible, we must adopt a constitutional construction of a statute. § 2-4-201(1)(a), 1B C.R.S. (1980), People v. Schwartz, 678 P.2d 1000 (1984).
*259In E.R.S. this court held that “[parents who protest the adoption of their children must be provided with ‘fundamentally fair procedures’ because natural parents have ‘a fundamental liberty interest in the companionship, care, custody and management of their child.’ ” E.R.S., 779 P.2d at 847, quoting R.H.N., 710 P.2d at 487. Thus, in interpreting these provisions we presume that the legislature acted with proper regard for parents’ fundamental interest in securing their relationship with their children. The plain language of section 19 — 5—203(1)(f) leads us to reject D.J. T.’s suggested construction of the statute. By phrasing the consent requirement for the adoption of children of unwed parents in the disjunctive “or," the legislature must have contemplated that in certain circumstances the consent of a single unwed parent would suffice whereas, in other circumstances, the consent of both parents should be required to permit the adoption of their child. A contrary interpretation would render the word “parents” completely superfluous, contrary to well-established principles of statutory interpretation, because the consent of a single “parent” would in every instance establish that a child is available for adoption. We believe that a more natural interpretation of the statute is that the consent of only one parent is sufficient when the other parent is deceased or the identity or whereabouts of the other parent is not known and not ascertainable by due diligence. This interpretation of section 19 — 5—203(l)(f) will protect the liberty interest of unwed parents in their relationship with their children. If both unwed parents are known and either is unwilling to consent, then the adoption proceeding may not go forward on the basis of subsection (l)(f). We hold that a child is not “available for adoption” under section 19 — 5—203(l)(f) without the consent of both natural parents when both parents are living and the identity and whereabouts of both parents are known or ascertainable by due diligence.
Because there is no dispute that D.J.T.’s identity and location were known in this case, the adoption of E.E.F. was only proper if D.J.T. validly consented to E.E.F.’s adoption. D.J.T. claims that although he consented to the adoption of E.E.F., his consent was conditioned upon his retaining the right to visit E.E.F. Because such right is unenforceable, D.J.T. argues, his consent must be invalidated. Further, D.J.T. argues that even if his consent to the adoption was valid, E.E.F.’s adoption must be set aside because he was not notified of the time and place of the adoption hearing.9 We disagree.
There is no dispute that D.J.T. accompanied S.O. and T.O. to visit the juvenile court in order to obtain information on the procedures for the adoption of E.E.F. Although they inquired of a clerk at the court whether it was possible to alter the standard adoption consent form to include terms granting D.J.T. visitation rights, D.J.T. proceeded to sign the unaltered consent form when he was told that form could not be altered. That form stated in relevant part:
I hereby consent to the adoption of said child by the petitioners in proceedings for such adoption which have been, or will hereafter be instituted in the Juvenile Court of Denver, Colorado, which adoption shall be subject to the approval and direction of the Judge of said Court.
Believing it to be for the best interest of said child, I do hereby give my consent freely and voluntarily to said adoption, and relinquish all my rights and claim to said child, and agree that from the date of the decree of adoption said child shall, to all legal intents and purposes, be the child of the person or persons so adopting said child.
I hereby waive any and all notice and notices required by law in connection with these proceedings and consent to the hearing of petition for the adoption *260of said child and the entry of final decree of adoption herein.
The juvenile court found that D.J.T.’s consent to the adoption of E.E.F. was “knowingly and intelligently and voluntarily” executed. Although the court did not explicitly determine that D.J.T. had knowingly and intelligently waived the right to notice in the adoption hearing, implicitly the court’s finding on the validity of the consent to the adoption applied equally with respect to the validity of the waiver of notice. There is sufficient evidence in the record to support the juvenile court’s finding that the consent to the adoption, and thus the waiver, was valid. First, we note that the consent/waiver form was written in plain language, clear and unambiguous on its face. D.J.T. consented to the relinquishment of “all my rights and claim to said child,” and agreed that the child would “to all legal intents and purposes, be the child of the person or persons so adopting said child.” Further, D.J.T. in his .testimony conceded that he was told by a court official that the consent form could not be changed to make the adoption conditional so as to grant him visitation rights. Also, T.O. testified that D.J.T. understood completely that his visitation rights would terminate under the agreement and that he would only be permitted to visit E.E.F. with S.O.’s and T.O.’s permission and that such permission would be granted only so long as D.J.T. did not use illegal drugs. Although there was conflicting evidence on this point, the juvenile court was free to reject D.J.T.'s claim that he signed the consent/waiver form only because he did not realize it would terminate his parental rights vis-a-vis E.E.F.10
Because D.J.T. validly consented to the adoption of E.E.F. by S.O., there was no basis upon which to grant his motion to set aside the adoption. A parent’s change of heart or subsequent regret at having consented to the adoption of his child is not by itself a sufficient reason for setting aside the adoption. B.B. v. S.S., 171 Colo. 534, 468 P.2d 859 (1970). Thus, because the juvenile court properly denied D.J.T.'s motion to set aside the adoption, the judgment of that court is affirmed.
Judgment affirmed.
QUINN, J., dissents, and ROVIRA, C.J., and ERICKSON, J., join in the dissent.. The appellees in their briefs now question whether the appellant properly brought this action under C.R.C.P. 60(b). Because this argument was not raised below, it is properly raised here only if the argument goes to the juvenile court’s jurisdiction to hear the matter. C.R.C.P. 60(b)(3) (motion to set aside judgment as void) only requires that the motion be brought within a reasonable time. Here, D.J.T. acted within a reasonable time after he was denied visitation. His action also was timely under section 19 — 5— 214, 8B C.R.S. (1989 Supp.), which requires an action challenging a final decree of adoption because of a jurisdictional or procedural defect to be brought within two years.
. T.O. and S.O. now assert in their brief that "(wjithout establishing paternity as provided by law, the father of a child born out of wedlock is without legal relationships to the child...." However, the appellees neither disputed DJ.T.’s paternity below nor challenged his standing to bring suit. On the contrary, they specifically acknowledged in the adoption hearing that D.J.T. was E.E.F.’s natural father and that he had consented to the adoption. Under well-established principles of appellate procedure, the appellees will not now be heard to challenge for the first time on appeal D.J.T.⅛ status as the natural father of E.E.F.
. D.J.T. testified that he visited E.E.F. three times per week, occasionally taking E.E.F. over to his parents’ house, and that he bought the child clothes. S.O. disputed some of this testimony; the trial court did not make a specific finding on this issue.
. E.E.F., prior to his adoption, bore the family name of his mother and not the name of his natural father, D.J.T.
. The record before us does not include the record of the injunction proceeding although the fact that an injunction was entered is not disputed.
. At the time this case was heard in the trial court, the adoption provisions were codified at sections 19-4-105 to -116, 8B C.R.S. (1986). In 1987, these sections were repealed and reenacted, and relocated to their present position in the statutes. Although there were some modifications in these provisions in 1987, those modifications are not relevant to the discussion before us. In considering D.J.T.’s challenge to our adoption provisions, we utilize the present statutory designations.
. Section 19-1-103(21), 8B C.R.S. (1989 Supp.), provides that a parent means either a natural parent of a child, as may be established under the Uniform Parentage Act, sections 19-4-101 to -129, 8B C.R.S. (1989 Supp.), or an adopted parent. Relevant here, section 19-4-105(l)(d) presumes a man to be the parent of a child if “[w]hile the child is under the age of majority, he receives the child into his home and openly holds out the child as his natural child.” Here, the appellees did not challenge D.J.T.’s parental status.
. In Stjernholm v. Mazaheri, 180 Colo. 352, 506 P.2d 155 (1973), we rejected the constitutional challenge of a natural father to a stepparent adoption under section 22-4-7(1), C.R.S. (1963) (1969 Perm.Supp.), now codified at section 19-5-203(l)(d)(II), 8B C.R.S. (1989 Supp.). The father in Stjernholm, who had divorced the child’s natural mother, apparently argued that principles of due process required his consent prior to the adoption of his child. The court, in rejecting his argument, found that the father’s nonsupport of his child could provide a basis for the adoption without his consent. As noted above, the adoption in this case did not proceed under the theory that the natural father had abandoned E.E.F.
. Although section 19 — 5—203(l)(f) does not specifically require that an unwed parent in the circumstances of D.J.T. be given notice and an opportunity to be heard at the adoption hearing, we have held previously that a parent’s liberty interest in his relationship with his child may not be adversely affected in a judicial proceeding unless the parent is provided with notice and an opportunity to be heard. Hamman v. County Court, 753 P.2d 743, 748 (Colo.1988).
. We question whether a parent, having executed a valid consent authorizing the adoption of his child, is in any event entitled to notice and an opportunity to be heard at the adoption hearing. Obviously, the purpose of notice and an opportunity to be heard is so that the parent might raise objections to the adoption of the child. Having consented to such adoption, presumably there is no longer any reason to notify the parent in advance of the legal proceedings intended to act upon such consent. See Smith v. Welfare Dept., 144 Colo. 103, 355 P.2d 317 (1960) (parents having validly relinquished child had no right to object to lack of notice of subsequent adoption hearing); see also Matter of Andersen, 99 Idaho 805, 589 P.2d 957 (1978), overruled on other grounds, Petition of Steve B.D., 111 Idaho 285, 723 P.2d 829 (1986) (valid unrevoked consent to adoption negates requirement of notice and opportunity to be heard).