'American Reunion:' Chris Klein Reveals 5 Plot Secrets From the Set (Exclusive)

Sam Jones/Universal Pictures

The actor, currently on FX's "Wilfred," opens up from the Atlanta set of the "American Pie" sequel about how the franchise has evolved and how he laughed off that infamous "Mamma Mia!" audition tape.

All the original cast members from American Pie are currently in Atlanta filming American Reunion, which hits theaters April 2012. Chris Klein, who plays Oz in the iconic high school film franchise, spoke to The Hollywood Reporter about who's shown up on set, how the anticipated comedy franchise has evolved and how to laugh off that infamous Mamma Mia! audition tape.

1. Oz is now a Hollywood hot shot
Klein's sensitive high school virgin (who bedded girlfriend Mena Suvari at the end of the first film) "has moved to a beach house in Malibu. He's found his way to Hollywood, where he works as a sportscaster on an NFL show. And he has a young girlfriend, Mia, played by [30 Rock's] Katrina Bowden, who is really, really funny," he says. "And he gets his invite to the reunion and decides to go with his girlfriend." Bowden and Suvari have a confrontation there. "I'm not sure yet how awkward it is… we haven't shot that yet. There's gotta' be a little awkwardness."

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2. They don’t always stick to script – so expect a few surprises
"There's a bit of ad-libbing and riffing that goes on. We're all having a really good time. The directors Jon [Hurwitz] and Hayden [Schlossberg] are really open," Klein says. "Watching an actor like Eugene Levy take everything Seann [William Scott] has, less than a foot from his face, while everyone else on set is literally biting their tongue…Yet all the while, he doesn't even break a sweat…and then they yell cut and we all come to pieces. It's like that, over and over for 12-14 hours a day… There's always hijinks when you get a bunch of people that like to do comedy together. We can't help ourselves. It's adult summer camp there. Twelve to 14 hours of laughter all the time. So I've been able to scale back my sit-up routine a little bit," he jokes.

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3. There's been a wedding and a baby
Alyson Hannigan's Michele and Jason Bigg's Jim have taken their relationship to the next level. "They're still married and are terrific. They have one [kid]," Klein says.

4. Stiffler hasn't exactly matured
"Stiffler is always Stiffler. He's having a good time," Klein laughs. "Seann, in this franchise, works harder than any of us being Stiffler…running and gunning. We find Stiffler back in East Great Falls, doing his thing. He's just trying to find his way in the world as this crazy guy." And Stiffler's mom -- Jennifer Coolidge -- "makes an appearance in the movie. You can't have an American Pie without Stiffler's mom!"

5. Expect to see the ENTIRE cast from the original — including Tara Reid and Shannon Elizabeth
"All the originals come back to say hello," says Klein. And they're all just as close as ever on set. "It's been so amazing to watch this cast mature over the last 10 years. There is a certain sense of pride I have for them all, like when I flip through the channels and see [How I Met Your Mother star] Alyson and I think, 'Oh man, she's doing fantastic.' I have felt that for all of them and still do. Even if we don't see each other for a couple of years, we could sit down and give each other a hug and catch right back up like we haven't missed a beat. It's pretty special."

6.  BONUS: Klein has a healthy sense of humor. He laughs off that infamous Mamma Mia! audition tape that went viral online
"Those auditions… we all take chances and sometimes push what our creative limitations are. I certainly did my best to do that. I went for it. I can see now after watching that audition why I didn't get the part!" he jokes. "I really like taking chances, pushing the envelope. It is what it is."

Klein also appears in Wilfred on FX (Thursdays, 10 p.m. ET)