Actor Michael Cera was left reeling in pain after Rihanna slapped him for a scene in new apocalyptic comedy movie This Is The End.

The film marks Seth Rogen's directorial debut and it features the likes of James Franco, Jonah Hill, Emma Watson and Cera playing exaggerated versions of themselves as the world begins to end.

In one scene, Cera slaps guest star Rihanna on the butt, prompting the singer to swipe the actor across the face - and Rogen insists the Umbrella hitmaker didn't hold back when she shot the sequence.

He tells, "Rihanna did slap the s**t out of him. For real, he said, 'I'm actually going to slap the s**t out of your a**,' and she was like, 'I'm actually going to slap the s**t out of your face then.'

"We did it like six times, and the last time, he was like, 'I don't think I can do this anymore.'"

Explaining how Rihanna ended up filming the cameo, Rogen adds, "I'd never met her before we made this movie. I read that some of her favourite movies were Superbad and Pineapple Express, and I just remembered it to make me feel good about myself. And then, years later, we were doing this and we were like, who could we get? And I was like, 'Rihanna!'"