Matthew Perry miraculously transforms into Zac Efron's body in the all-new comedy '17 Again,' in theaters April 17, and Zac spills the beans on what it's like to go back to high school again, and what it was like to kiss his longtime crush Leslie Mann.

"Matthew said something today that pretty much described me in high school as well," Zac Says. "He said he was the coolest of the geeks. I definitely was not the cool guy in school."

Zac also opened up about his onscreen lip lock with Leslie Mann who he admits to having a crush on from a young age.

"At first on paper that was one of the weirdest parts of the movie to kind of wrap my head around," Zac says. "Then Leslie signed on to the movie and I was stoked. She's awesome and beautiful and I've had a crush on her since I was 10 years old."

In '17 Again,' Matthew plays a thirty something father and husband whose once-bright future was sidelined by his girlfriend's pregnancy. Now almost 20 years out of high school, his teenage kids think he's a loser, he's been passed over for a promotion and he's in the doghouse with his wife (Mann).

Yearning for his glory days, his wish to be 17 again miraculously comes true and his body is transformed back to its prime (played by Zac). But can his severely dated outlook make the cut with the class of 2009?

Leslie also talked to ET about her romantic scene with Zac watch the video to find out what her young daughter did after she told about the kiss!

Watch ET for more with Zac!