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Kevin James unleashes his inner ultimate fighter in the new comedy Here Comes the Boom, in theaters Friday, and he tells ET about his "brutal" training and diet and adrenaline-fueled fight scenes.

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"Me getting into that octagon against a real UFC fighter … once we start [cameras] rolling and going at it, and adrenaline is involved, it's a rush that's I've never experienced in my life," explains Kevin.

In Here Comes the Boom, Kevin plays a devoted high school biology teacher and former wrestler who steps into the mixed-martial-arts ring in order to raise enough cash to rescue his school's music program.

Kevin co-wrote and produced the action-comedy, which also stars Salma Hayek and Henry Winkler, and he says getting into fighting shape for the picture was brutal mainly because of his restrictive diet – and lack of pizza for the self-proclaimed "pizza freak."

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He jokes: "The diet was tough and I thought, 'Man, this diet is the worst thing ever. This is the hardest part about doing this movie.' Then I got punched in the face. Then I go, 'No, this is the hardest part. I don't like this anymore.'"