PLURALITY OPINION
JOHN S. ANDERSON, Justice.The Attorney General of Texas appeals the trial court’s order modifying a prior order of child support that decreases the monthly child support obligation owed by appellee, Roosevelt P., from $420 to zero. The Attorney General contends the trial court erred by admitting into evidence and considering paternity results when it modified Roosevelt’s child support obligation because: (1) collateral estoppel and res judicata barred the issue of paternity from being relitigated; (2) the Uniform Parentage Act precluded Roosevelt from rebutting his presumption of paternity; and (3) the paternity results failed to meet the admissibility requirements of the Texas Family Code. We reverse and remand.
I, Factual and Procedural Background
Roosevelt married Anita in June of 1988, and they lived together as husband and wife until they separated on March' 12, 1991. On July 16, 1991, four months after their separation, Anita gave birth to R.J.P. Anita and Roosevelt remained separated *183without court ordered child support until 1998. In April of 1998, in cause number 98-14343, the trial court signed an agreed child support order finding Roosevelt to be R.J.P.’s biological father and ordering him to pay monthly support payments of $205.
In January of 2003, as a result of Roosevelt’s increased earning capacity, the Attorney General, in cause number 98-14343, sought to modify Roosevelt’s monthly child support obligation from $205 to $420. After receiving notice of the requested modification, Roosevelt secured a private paternity test for himself and R.J.P. On March 18, 2003, Roosevelt received the paternity results which he claims prove he is not the biological father of R.J.P. On March 21, 2003, Roosevelt filed an original petition for divorce with the trial court under cause number OS-14736, a different cause number than the Attorney General’s motion to modify. On May 19, 2003, the trial court, without receiving a request for a hearing or a response from Roosevelt to the Attorney General’s motion to modify, increased Roosevelt’s monthly child support obligations from $205 to $420 in accordance with the Attorney General’s request.
On June 9, 2003, Roosevelt filed an amended divorce petition seeking to voluntarily terminate the parent-child relationship. Contemporaneously, Roosevelt filed a motion under cause number 98-14343 seeking to. terminate child support and withholding based on his claim that he is not the biological father of R.J.P. On November 5, 2003, the trial court consolidated both cause numbers into cause number 98-14343.
At a hearing on the matter, the trial court took judicial notice of the entire contents of the files in the case, including the 1998 order establishing Roosevelt’s biological paternity. Afterwards, Roosevelt sought to introduce paternity results establishing he is not the biological father of R.J.P. Over the Attorney General’s objections, the trial court admitted the paternity results into evidence.1 Contemporaneously, the trial court ordered Roosevelt, Anita, and R.J.P. to submit to a court ordered paternity test before the next hearing. In support of its order to obtain genetic testing, the trial court stated:
It think it’s very important that we establish, without any doubt, for any party, Mom or Dad or your child, who her father is. There is [sic] good health reasons if she ever needs to have any sort of transplant-type stuff for us to have a bone marrow transplant, it’s so important to know that a whole other family might exist to be possible donors of, both, of anything that may be needed from a health standpoint.
*184At the follow-up hearing, the trial court learned that Anita and R.J.P. failed to obtain the court ordered genetic test, and over objection, the trial court re-admitted the privately secured paternity results into evidence.2 On February 20, 2004, the trial court granted the parties a divorce, eliminated withholding, and decreased Roosevelt’s monthly child support obligation from $420 to zero without changing Roosevelt’s status as R.J.P.’s father.3 To support the modification, the trial court’s amended findings of fact and conclusions of law state Roosevelt “may not be the biological father of the minor child.”
II. Discussion
On appeal, the Attorney General contends the trial court erred when it modified Roosevelt’s monthly child support obligation to R.J.P. from $420 to zero because the determination was based on inadmissible paternity results. Specifically, the Attorney General contends the trial court should .not have considered the paternity results because collateral estoppel and res judicata bar the issue of parentage from being relitigated because the paternity results contradict a court order almost five years earlier.
A. Standard of Review
In determining questions of child support, the trial court’s primary consideration must always be the best interest of the child. Clark v. Jamison, 874 S.W.2d 312, 316 (Tex.App.-Houston [14th Dist.] 1994, no writ). Trial judges have wide discretion with respect.to child support. Dennis v. Smith, 962 S.W.2d 67, 68 (Tex.App.-Houston [1st Dist.] 1997, pet. denied). Questions concerning the admission and exclusion of evidence are reviewed under an abuse of discretion standard. City of Brownsville v. Alvarado, 897 S.W.2d 750, 753 (Tex.1995). We will reverse only if the trial court abused its discretion by acting without reference to any guiding rules or principals or by acting arbitrarily or unreasonably. City of San Benito v. Rio Grande Valley Gas Co., 109 S.W.3d 750, 757 (Tex.2003); Worford v. Stamper, 801 S.W.2d 108, 109 (Tex.1990). A trial court has no discretion in deciding what law applies or in applying the law to the facts of the case. In re Kuntz, 124 S.W.3d 179, 181 (Tex.2003) (orig.proceeding); accord In re D.S., 76 S.W.3d 512, 516 (Tex.App.Houston [14th Dist.] 2002, no pet.) (failing to analyze or construe law correctly constitutes abuse of discretion). We will not *185reverse a trial court for an erroneous evi-dentiary ruling unless the error probably caused the rendition of an improper judgment. See Tex.R.App. P. 44.1(a)(1); Owens-Corning Fiberglas Corp. v. Malone, 972 S.W.2d 35, 43 (Tex.1998).
B. Was Biological Paternity Adjudicated in an Earlier Proceeding?
Paternity, although uncontested, was an issue addressed and resolved by the trial court in the 1998 Suit Affecting the Parent Child Relationship. The agreed order establishes Roosevelt and Anita as “the biological parents” of R.J.P. and provides for child support, conserva-torship, and visitation. An agreed order “is accorded the same degree of finality and binding force as a final judgment rendered at the conclusion of an adversary proceeding.” McCray v. McCray, 584 S.W.2d 279, 281 (Tex.1979); see Tex. Fam. Code Ann. § 160.637(a)(2) (Vernon 2002) (stating a determination of parentage is binding on all parties to an adjudication by a court acting under circumstances satisfying the jurisdictional requirements of Texas Family Code section 159.201). Thus, the finding within the 1998 order that Roosevelt is the biological father of R.J.P. has been adjudicated and has the binding effect of a final judgment rendered at the conclusion of an adversary proceeding.
C. Was the Adjudicated Fact Properly Challenged?
According to section 160.637(e) of the Texas Family Code, Roosevelt can only challenge the adjudicated fact of biological paternity “under the laws of this state relating to appeal, the vacating of judgments, or other judicial review.” Tex. Fam. Code Ann. § 160.637(e) (Vernon 2002). Roosevelt did not file any motions with the trial court after the 1998 adjudication, did not challenge the 1998 order on appeal, and he did not file a bill of review. See Tex.R. Civ. P. 329b(d), (f). Because Roosevelt did not challenge the 1998 order adjudicating his biological paternity “under the laws of this state,” we must determine whether the trial court was barred from relitigating Roosevelt’s biological paternity in determining his child support obligation.
D.Was the Trial Court Barred from Relitigating Biological Paternity?
To bar an action on the basis of collateral estoppel, the movant must prove the following elements: (1) the same fact issue from the first suit is sought to be litigated in the second suit; (2) the fact issue was essential to the judgment in the first suit; and (3) the parties were cast as adversaries in the first suit. In re T.S.S., 61 S.W.3d 481, 485 (Tex.App.-San Antonio 2001, pet. denied) (citing Johnson & Higgins of Tex., Inc. v. Kenneco Energy, 962 S.W.2d 507, 521 (Tex.1998)).
The doctrine of collateral estoppel bars relitigation of biological paternity in a subsequent suit. See Dreyer v. Greene, 871 S.W.2d 697, 697-98 (Tex.1993) (holding trial court’s adjudication of biological paternity within a divorce decree barred any subsequent assertion of parentage to the contrary); In re T.S.S., 61 S.W.3d at 485 (holding collateral estoppel barred father from relitigating a paternity finding in divorce decree with DNA results as a defense to paying child support); Byrd v. Travelers Ins. Co., 275 S.W.2d 861, 863 (Tex.Civ.App.-San Antonio 1955, writ ref d n.r.e.) (holding parents of deceased worker were barred from relitigating a paternity finding in divorce decree which found their son had fathered a son during his marriage); see also Tex. Fam.Code Ann. § 159.315 (Vernon 2002) (providing that “[a] party whose parentage of a child has been previously determined by or under law may not plead nonparentage as a defense to a proceeding under [the Uniform Interstate Family Support Act]”); Baize v. *186Baize, 93 S.W.3d 197, 201 (Tex.App.-Houston [14th Dist.] 2002, pet. denied) (recognizing the principals of res judicata and collateral estoppel but distinguishing the facts because the issue of paternity was raised before the trial court signed a final judgment). Consistent with the aforementioned cases, the doctrine of collateral es-toppel barred Roosevelt from relitigating the finding that he is the biological father of R.J.P.
This issue of biological paternity could have been litigated in 1998. By his own admission, Roosevelt harbored doubts about his biological paternity to R.J.P. in 1997-and could have obtained genetic testing before he signed the 1998 order? however, he chose not to do so. Roosevelt did not challenge his adjudication of biological paternity until eleven years after R.J.P.’s birth- and more than four years after the 1998 original adjudication. In the aftermath of an increased child support obligation, Roosevelt sought to relitigate the previously adjudicated fact issue.- The 1998 judgment at issue in this case “should not be set aside bécause one of the individuals involved has become unhappy with the continued existence of it.” Ince v. Ince, 58 S.W.3d 187, 191 (Tex.App.-Waco 2001, no pet.).
We conclude collateral estoppel barred the issue of Roosevelt’s biological paternity from being relitigated in this suit because: (1)Roosevelt’s biological paternity was litigated in a prior suit; (2) the issue of Roosevelt’s paternity was essential to the 1998 judgment; and (3) the same parties were cast as adversaries in the first suit.4 Thus, the trial court abused its discretion when it considered the paternity results in its determination of Roosevelt’s. child support obligation.
E. Was the Trial Court’s Consideration of Paternity Harmful Error?
To rebut the child support guidelines presumed to be in the best interest of the child, pursuant to section 154.123 of the Texas Family Code, the trial court’s amended findings of fact and conclusions of law considered the following:
(1) That the minor child was not residing with [Anita], but has been residing with her aunt since June, 2003, in the State of Tennessee and is enrolled in School in Tennessee, while both parents reside in Houston, Harris County, Texas;
(2) That [Roosevelt] has been unable to exercise visitation consistently with the minor child since June of 2003;
(3) That [Roosevelt] was only furnished the . child’s telephone number after an August 27, 2003, hearing in this matter and- had not known the whereabouts of the child or how to contact the child. The Court ordered [Anita] to produce the telephone number of the child; and,
*187(4) That Petitioner, [Roosevelt], may not be the biological father of the minor child ...
See Tex. Fam.Code ANN. § 154.123 (Vernon 2002).
We hold the trial court’s erroneous consideration of biological paternity in this case was harmful, in that it probably caused the rendition of an improper judgment. We can find no basis in the record supporting the trial court’s determination that modifying Roosevelt’s child support obligation to zero dollars is in R.J.P.’s best interest. See Tex.R.App. P. 44.1(a). We sustain appellant’s first issue.
III. CONCLUSION
Having found harmful error, we reverse the portion of the trial court’s judgment modifying Roosevelt’s child support obligation to zero and remand for further proceedings.5 Because of our disposition of appellant’s first issue, we need not address appellant’s other issues.
YATES, J. concurs in result only.
HUDSON, J. dissents.
. The Attorney General did not plead res judi-cata or collateral estoppel as an affirmative defense in its answer to Roosevelt’s petition as required by Texas Rule of Civil Procedure 94. See Tex.R. Civ. P. 94 (requiring party to plead affirmative defenses in pleading to a preceding pleading). However, Roosevelt did not object when the Attorney General orally objected to the introduction of the paternity results at trial based on its prior adjudication. Because Roosevelt did not object, the affirmative defenses of res judicata and collateral estoppel were tried by consent of the parties. See Tex.R. Civ. P. 67; Mastin v. Mastin, 70 S.W.3d 148, 154 (Tex.App.-San Antonio 2001, no pet.) (holding the affirmative defense of notice was tried by consent where husband did not plead notice as a defense and wife did not object to lack of pleadings when the defense was argued at trial); Whitley v. Whitley, 566 S.W.2d 660, 662 (Tex.App.-Beaumont 1978, no writ) (holding the affirmative defense of res judicata was tried by consent when it was not properly raised in husband's pleadings because wife did not object to husband’s oral plea of res judicata as being improperly pled).
. The record reveals R.J.P. moved to Tennessee at the end of June 2003 to live with Anita’s sister for the summer and the following school year. The trial court was aware when it issued the October 2003 genetic testing order that R.J.P. would be available to receive the genetic testing over the Christmas holidays while she was visiting Houston.
. The divorce decree conflicts with the trial court’s amended findings of fact and conclusions of law. Under the heading "CHILD SUPPORT,” the divorce decree orders "that Respondent shall not be required to pay child support effective from the 9th day of June, 2003.” (emphasis added). The first paragraph of the divorce decree identifies Anita as the Respondent and Roosevelt as the Petitioner. Therefore, the "four corners” of the divorce decree does not, in fact, reduce Roosevelt’s monthly child support obligation to zero.
However, the trial court’s amended findings of fact and conclusions of law filed after the judgment clearly establish that Roosevelt's child support obligation is terminated. Findings of fact and conclusions of law filed after a judgment are controlling if they conflict with a previous judgment.' Capital Senior Mgmt. 1, Inc., v. Tex. Dep't of Human Servs., 132 S.W.3d 71, 74 n. 3 (Tex.App.-Austin 2004, pet. denied); Dickerson v. DeBarbieris, 964 S.W.2d 680, 684 (Tex.App.-Houston [14th Dist.] 1998, no pet.). Therefore, Roosevelt’s monthly child support obligation was modified.
. The dissent, without any authority, contends reliance on collateral estoppel and'res judica-ta are inappropriate in the context of a parent-child relationship because, for example, the trial court maintains continuous, exclusive jurisdiction and has the authority to modify the terms of that relationship as changing circumstances require. I respectfully disagree that litigation of biological paternity is a changing circumstance. As discussed herein, biological paternity could have been litigated in 1998. Allowing parties to relitigate this issue would burden the courts and traumatize the child, an outcome this court should not sanction. See, e.g., John G. and Marie Stella Kenedy Mem'l Found, v. Dewhurst, 90 S.W.3d 268, 288-89 (Tex.2002) ("[Rjes judicata and collateral estoppel both serve 'the dual purpose of protecting litigants from the burden of relitigating an identical issue with the same party or his privy and of promoting judicial economy by preventing needless litigation.' ” (quoting Parklane Hosiery Co., Inc. v. Shore, 439 U.S. 322, 326, 99 S.Ct. 645, 649, 58 L.Ed.2d 552 (1979))).
. If the error affects only part, but not all of the case, a judgment may be reversed only as to the part affected by the error. See Tex.R.App. P. 44.1(b); see also Tex.R.App. P. 61.2.