Seth Rogen
is a big fan of Zac Efron

The hilarious actor sat down with Conan O'Brien on Tuesday's "Conan" where he opened up about filming "Neighbors" with the former Disney star.

Check out the video above to see what Seth had to say about Efron's super sexy muscles!

"I would just look at it and want to reach out and touch it," Rogen said about his costars body. "He's the sexiest mother f--ker alive!," Seth added. 

We can't blame the "Knocked Up" star for being fascinated with the 26-year-old's impressive physique. Zac looks pretty damn good shirtless, that's for sure! 

Make sure to check out the twosome's latest flick, "Neighbors," when it hits theaters May 9 -- and see our interview with their costar, Dave Franco, in the video below:

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