New apocacomedy "This Is the End" may be based on the (hopefully) fictitious end of the world, but one part of the movie definitely was real: Michael Cera's sore face.

In the red band trailer for "This Is the End," the twee Canadian slaps pop dinger Rihanna's read, and she gives him a smack of her own — across the face. So much for stage fighting, as Seth Rogen, one of the film's stars, revealed to MTV News' Josh Horowitz that the slap was real. And hard.

"Rihanna did slap the s**t out of him, for real," Rogen said at a panel for MTV's Sneak Peek Week, a week of first looks at this summer's blockbusters, leading up to the 2013 MTV Movie Awards this Sunday.

"We did it like six times, and then the last time we did it, he was like, 'I don't think I can do this again'," Rogen said of Cera.

"This Is the End" is due in theaters June 14.

Stay tuned to MTV's Sneak Peek Week every evening from now until Sunday for the first looks at this summer's biggest movies, and don't forget to tune into the 2013 MTV Movie Awards on Sunday at 9 ET to join in the fun.