JUSTICE APPLETON delivered the opinion of the court:

Defendant, Verle W. Uptain, was convicted of threecounts of aggravated criminal sexual abuse and was sentenced toconcurrent three-year terms of imprisonment. On appeal, heclaims the trial court erred in refusing to give the jury aninstruction stating that it is a defense to the charge thatdefendant reasonably believed the victim was at least 17 yearsold. He also claims the statute requiring him to register as asex offender (730 ILCS 150/7 (West 2000)) for the rest of hislife is unconstitutional as applied to him. We reverse andremand.

I. BACKGROUND

On August 30, 2001, defendant was charged with twocounts of criminal sexual assault (720 ILCS 5/12-13(a)(1) (West2000)) and three counts of aggravated criminal sexual abuse (720ILCS 5/12-16(d) (West 2000)) for a July 9, 2001, incident involving S.M., defendant's 16-year-old neighbor. According to trialtestimony, S.M. went to defendant's trailer on the evening ofJuly 9, 2001, to visit and watch television. As she arrived,defendant's wife, son, and granddaughter were leaving to go tothe store. Defendant and his daughter, Christina, were at homein the living room watching television. Defendant was seated onthe loveseat, and Christina was seated on the couch. When S.M.came in, she sat next to defendant on the loveseat. S.M. disputed the testimony that she tickled, grabbed, and poked defendant and tried to twist his nipples while they watched television. She also disputed testimony that she pulled defendant'sright arm around her shoulder and placed his hand on her breast.

Christina left the living room leaving defendant andS.M. on the loveseat. After defendant's daughter left the room,defendant asked S.M. if she wanted to go for a ride in histractor-trailer. S.M. had expressed such a desire on previousoccasions. The two walked to where the truck was parked down thestreet. S.M. lay down on the bed in the sleeper portion of thetruck. She did not sit on the passenger seat for two reasons:there was too much clutter on the seat and the trucking companywould not allow any passenger in the truck without prior authorization.

Defendant drove for approximately five minutes and thenparked the truck in a parking lot. He retrieved a window shadeand snapped it around all of the windows, then went to thesleeper portion of the cab and lay on S.M. He pulled up hershirt and bra and began kissing her breasts, chest, and stomach. He ripped her skirt while trying to pull it off. He then realized it had a zipper, unzipped it, and took it off. He removedher underwear, briefly inserted his finger in her vagina, put histongue in her vagina, and then penetrated her with his penis. Thereafter, the two got dressed, and defendant drove home.

S.M. went back to defendant's trailer and, as defendanttold her to do, informed defendant's wife she and defendant hadgone to get something for his trailer. Christine told S.M. thather father had been looking for her and she needed to go home. S.M. told a friend, and later the police, of the incident thenext day.

The jury found defendant guilty of three counts ofaggravated criminal sexual abuse--acts of sexual penetration witha victim who was between 13 and 17 years old and the accused wasat least 5 years older than the victim (720 ILCS 5/12-16(d) (West2000)). The jury acquitted defendant of two counts of criminalsexual assault--acts of sexual penetration by the use of force orthreat of force (720 ILCS 5/12-13(a)(1) (West 2000)). The trialcourt sentenced defendant to concurrent three-year terms ofimprisonment and denied his posttrial motion. This appealfollowed.

II. ANALYSIS

A. Jury Instruction

Defendant first argues that the trial court erred inrefusing to give Illinois Pattern Jury Instructions, Criminal,No. 11.64 (4th ed. 2000) (hereinafter IPI Criminal 4th), whichinstructs the jury it is a defense to the crime charged thatdefendant reasonably believed S.M. was 17 years old. IPI Criminal 4th No. 11.64 is based on section 12-17(b) of the CriminalCode of 1961 (720 ILCS 5/12-17(b) (West 2000)) and operates as anaffirmative defense. Defendant claims the court erred in refusing to tender the instruction because (1) S.M. was 16 years old--the upper end of the offense range, (2) there was some evidencethat she engaged in adult-type sexual behavior on the evening inquestion, and (3) the jury, after seeing S.M.'s appearance anddemeanor, could have reasonably believed she was 17 years old. Defendant claims the failure to give the instruction left himwith no defense to the charges. Defendant relies solely onPeople v. Jones, 175 Ill. 2d 126, 676 N.E.2d 646 (1997), tosupport his claim of error.

In Jones, 175 Ill. 2d at 128-29, 676 N.E.2d at 647, thedefendant was convicted of attempt (aggravated criminal sexualabuse). At trial, the victim, D.R., testified that at the timeof the incident he was 16 years and 10 months old. D.R. and twofriends met Jones at a party where the four spent the eveningdrinking beer together. The sexual incident occurred in abedroom after the two friends fell asleep.

Jones challenged the sufficiency of the evidencesupporting his conviction and claimed he did not receive a fairtrial because, inter alia, the trial court erroneously refusedhis tendered jury instruction on the affirmative defense that hehad a reasonable belief D.R. was at least 17 years old. Jones, 175 Ill. 2d at 131, 676 N.E.2d at 648. This court affirmed thetrial court's decision, finding insufficient evidence was presented to fairly raise the issue of the affirmative defense. Jones, 175 Ill. 2d at 131, 676 N.E.2d at 648. However, thesupreme court, agreeing with Justice Cook's dissent, found it wasreversible error to prevent Jones from presenting his defense bymeans of the tendered instruction. Jones, 175 Ill. 2d at 131,676 N.E.2d at 648.

The supreme court found the following circumstantialevidence was sufficient to allow the jury to determine whether itwas reasonable for Jones to believe D.R. was at least 17 yearsold: (1) D.R. was 16 years and 10 months old, (2) Jones did notknow D.R. before the incident, (3) D.R. was consuming alcohol,and (4) D.R. was free to stay overnight at his friend's apartment. Additionally, the jury saw D.R. testify and was able toobserve his appearance and demeanor. The court held that"[a]bsent [the] defendant's tendered instruction, the jury lackedthe necessary tools to analyze the evidence fully and to reach averdict based on those facts." Jones, 175 Ill. 2d at 134, 676N.E.2d at 650.

"A defendant is entitled to an instruction on histheory of the case if there is some foundation for theinstruction in the evidence, and if there is such evidence, it isan abuse of discretion for the trial court to refuse to soinstruct the jury." Jones, 175 Ill. 2d at 131-32, 676 N.E.2d at649. Very slight evidence upon a given theory of a case willjustify the giving of an instruction. Jones, 175 Ill. 2d at 132,676 N.E.2d at 649. To avail himself of the affirmative defenseat issue, a defendant is required to produce some evidence attrial to demonstrate the existence of a reasonable belief thatthe victim was 17 years of age or older. Jones, 175 Ill. 2d at132, 676 N.E.2d at 649.

However, the defendant will be excused from presentingany evidence where the evidence presented by the State raises theissue of the affirmative defense. Jones, 175 Ill. 2d at 132, 676N.E.2d at 649. In essence, unless the evidence before the trialcourt is so clear and convincing as to permit the court to findas a matter of law that there is no affirmative defense, theissue of whether a defendant should be relieved of criminalliability by reason of his affirmative defense must be determinedby the jury with proper instruction as to the applicable law. Jones, 175 Ill. 2d at 132, 676 N.E.2d at 649.

We cannot say the evidence here was so clear andconvincing as to justify a failure to instruct the jury as towhether defendant should be relieved from criminal liabilitybased upon his reasonable belief of S.M.'s age. The Statepresented the following evidence: (1) S.M. was 16 years old atthe time of the incident and at the time of trial, (2) S.M. livednext door to defendant for one to two years prior to theincident, and (3) defendant never told Officer Arnold that he wasconfused about S.M.'s age. No evidence showed that defendant hadever been advised of S.M.'s actual age.

Defendant was not required to present any evidence thathe believed S.M. was at least 17. See Jones, 175 Ill. 2d at 133,676 N.E.2d at 649. The evidence he did present--that S.M.engaged in playful and flirtatious behavior on the evening inquestion--coupled with the evidence presented by the State wassufficient to raise the affirmative defense. Noting that only"[v]ery slight evidence" upon a given theory justifies giving theinstruction, we find the testimony presented sufficientlyqualifies as enough to present the question to the jury. SeeJones, 175 Ill. 2d at 132, 676 N.E.2d at 649.

The jury should have been given the opportunity,considering the evidence presented and viewing S.M.'s appearanceand demeanor, to determine whether defendant had a reasonablebelief that S.M. was 17. We are mindful that our role at thisstage is not to weigh the evidence but only to determine whethersome evidence supported the theory. See Jones, 175 Ill. 2d at132, 676 N.E.2d at 649. Thus, we hold that by refusing the juryinstruction, the trial court effectively denied defendant dueprocess and, as such, he is entitled to a new trial.
 

B. Registration as Sex Offender

Defendant next contends that the Sex OffenderRegistration Act (730 ILCS 150/1 through 12 (West 2000)), whenapplied to his case, is unconstitutional as a violation of equalprotection. Because we have determined above that defendant isentitled to a new trial, we decline to consider hisconstitutional argument, which is based solely upon the outcomeof his first trial and may not apply after retrial. See Mattisv. State Universities Retirement Systems, 212 Ill. 2d 58, 75, ___N.E.2d ___, ___ (2004) (courts will not address constitutionalissues that are unnecessary for the disposition of the case underreview).

III. CONCLUSION

For the reasons stated, we reverse the conviction andsentence and remand this cause to the trial court for a newtrial.

Reversed and remanded.

COOK and STEIGMANN, JJ., concur.