Justice VOLLACK
specially concurring in the result only:
The majority holds that “[t]he jury was in effect instructed on, and convicted Rowe of, an offense that does not exist.” Maj. op. at 493. I agree; I write separately, however, to address the gravamen of the second issue upon which we granted certiorari. Unlike the majority, I find that the district court committed reversible error in this case by granting the prosecution an instruction containing a mitigating factor at the close of the evidence.
I.
As the majority notes, we granted certio-rari to address the following two issues:
Whether assault in the first degree committed in the heat of passion, § 18 — 3— 202(2)(a), 8B C.R.S. (1986), is a lesser non-included offense of assault in the first degree, § 18-3-202(l)(a), 8B C.R.S. (1986).
Whether the prosecution is entitled to request, despite the objection of the defendant, that a jury be instructed on the lesser non-included offense of assault committed in the heat of passion.
In response to the first issue, I agree with the majority that first-degree assault committed in the heat of passion is not a lesser nonincluded offense of first-degree assault because “there is no chargeable offense of first-degree assault committed under heat of passion.” Maj. op. at 490. I also agree with the proposition that “there is only one single crime of first-degree assault, albeit one that may have different sentences depending on whether the mitigating factor of heat of passion has been established.” Id. at 490-91. I find, however, that heat of passion functions like an affirmative defense regardless of whether the Colorado General Assembly has sought to define it as such. Accordingly, because heat of passion admits the doing of the act charged, but seeks to lessen liability for that act, only the defendant may request an instruction on it at the close of evidence.
*495A.
An affirmative defense is one which tends to “negative guilt by canceling out the existence of some required element of the crime.” Wayne R. LaFave & Austin W. Scott, Jr., Substantive Criminal Law § 1.8, 71 (1986); see People v. Huckleberry, 768 P.2d 1235, 1238 (Colo.1989) (“[A]n affirmative defense basically admits the doing of the act charged but seeks to justify, excuse or mitigate it.”). First-degree assault is a specific intent crime: it requires that a defendant act either with an intent to cause serious bodily injury, or with an intent to disfigure, or with knowledge that his or her conduct will create a grave risk of death to another person. § 18-3-202(1), 8B C.R.S. (1986). First-degree assault, as defined in section 18-3-202(1), is a class 3 felony. § 18-3-202(2)(b). Conversely, in a case of “heat of passion,” if the assault in the first-degree is “committed under circumstances where the act causing the injury is performed, not after deliberation, upon a sudden heat of passion, caused by a serious and highly provoking act of the intended victim, affecting the person causing the injury sufficiently to excite an irresistible passion in a reasonable person,” it is a class 5 felony. § 18-3-202(2)(a), 8B C.R.S. (1986). Thus, heat of passion is like an affirmative defense insofar as it tends to negate the fact that a defendant had the requisite specific intent or acted after deliberation.
Heat of passion additionally resembles an affirmative defense insofar as, once some credible evidence on that issue is raised, then the burden to prove a lack of provocation falls on the prosecution. See § 18-1-407, 8B C.R.S. (1986) (“‘Affirmative defense’ means that unless the state’s evidence raises the issue involving the alleged defense, the defendant, to raise the issue, shall present some credible evidence on that issue.”); LaFave & Scott, supra, at 72 (“[I]t is uniformly held that the defendant is obliged to start matters off by putting in some evidence in support of his defense.”). Under Colorado Criminal Jury Instruction Number 10:20, “[i]t is the burden of the prosecution to prove beyond a reasonable doubt a lack of provocation for the defendant’s acts.” 1
Whether heat of passion may be characterized as a “mitigating factor,” or as an affirmative defense, the prosecution should not be permitted to add charges via tendered jury instructions at the close of evidence; such conduct prejudices the defendant’s substantial right to notice of the crimes charged.2
B.
In the present case, the prosecuting attorney charged Rowe with first-degree assault in an information. At the close of the evidence at Rowe’s trial, Rowe tendered an instruction on second-degree assault committed under heat of passion, upon which his theory of the case was premised. The prosecution subsequently tendered instructions on second-degree assault and on first-degree assault committed under heat of passion. The district court gave all of the above-mentioned instructions to the jury. The district court’s action constitutes reversible error.
“The right of an accused to notice of the charges which have been made against him constitutes a fundamental constitutional guarantee and lies at the foundation of due process of law.” People v. Cooke, 186 Colo. 44, 46, 525 P.2d 426, 428 (1974). “Where a defendant acquiesces in placing a *496lesser crime before the jury, the requested instruction allows the jury to consider fully the elements of the crime charged and of the offense the defendant contends was involved.” People v. Rivera, 186 Colo. 24, 29, 525 P.2d 431, 434 (1974). Constitutional notice requirements, however, “preclude the submission of such an instruction at the request of the district attorney or by the court.” Id. at 28, 525 P.2d at 434. “It would be haphazard and unfair to say to a defendant that he must defend on the principal charge and any other charge which the evidence established.” Id. at 27, 525 P.2d at 434 (emphasis added). Accordingly, an information may only be amended as to form before the verdict “if no additional or different offense is charged and if substantial rights of the defendant are not prejudiced.” Crim.P. 7(e).
Only Rowe, and not the prosecuting attorney, could submit an instruction at the close of evidence on a heat of passion theory, thereby seeking to mitigate the level of the offense. The prosecution originally charged Rowe only with first-degree assault, a class 3 felony. Thus, at the time the information was filed, Rowe was put on notice that he was required to defend against a class 3 felony. The prosecution attempted to cast first-degree assault by heat of passion, a class 5 felony, as a different charge than first-degree assault, a charge against which Rowe did not have notice to defend, and a charge added without Rowe’s consent after the conclusion of the trial. Rivera and Cooke dictate that only the defendant is entitled to invoke the benefit of heat of passion “mitigation” at the close of trial.
I agree with the majority’s conclusion that a new trial is warranted in this case.
I am authorized to say that LOHR and KIRSHBAUM, JJ. join in this special concurrence in the result only.
. As a matter of practical consequence, a prosecutor will not endeavor to prove the four elements of heat of passion, see People v. Garcia, 826 P.2d 1259, 1262 (Colo.1992), in order to sustain a first-degree assault conviction — a class 5 felony — when a conviction of second-degree assault — a class 4 felony — may be more easily established. Cf. §§ 18-3-202(2)(a), -203, 8B C.R.S. (1986).
. I recognize that the prosecution may submit instructions on lesser included offenses at the close of the evidence, which the district court, in its discretion, may give to the jury. See People v. Cooke, 186 Colo. 44, 525 P.2d 426 (1974); Crim.P. 31(c). I agree with the majority, however, that first-degree assault by heat of passion is not a lesser included offense of first-degree assault. See maj. op. at 490.