Rihanna ‘concussed’ Michael Cera after he ‘slapped her a**’ while filming movie

I'm never one to judge a book by its cover but Rihanna and Michael Cera feel like chalk and cheese in the celebrity world.

The latter shot to fame after starring in Juno and Superbad back in 2007 when he was just a teenager, with his mum even forced to leave the set pretty quickly after seeing what he got up to in one of the scenes from the iconic comedy.

Cera also almost ended up getting married and then subsequently divorced from his Scott Pilgrim vs. the World co-star Aubrey Plaza, which suggests that his rock and roll attitude from that film is perhaps more of a reflection on his real life persona than most people give him credit for.

And, during a cameo appearance in This Is The End, Cera portrayed a coked-up sexual deviant who had Mindy Kaling weak at the knees, but it was the Barbie star who was left feeling worse for wear after his brief encounter with singing sensation Rihanna during the film.

Pretty much all the violence we see in films is fake, but Cera had the cheek (pardon the pun) to ask Rihanna if he could 'slap her a** for real' and the two agreed on a deal.

Film director Seth Rogen told Sway’s Universe: “In the script, Michael Cera slaps Rihanna's ass and she doesn't hit him back.

“But he asked her, ‘Can I slap your ass for real?’ And she said, 'You can slap my ass for real if I can slap you back in the face for real.'"

Rogen reports they did the scene ‘three or four times’ and that she ‘smacked the f**k’ out of Cera.

“She cupped his ear and actually whacked out his equilibrium and he had to go lay down in his trailer for around half an hour.

"That's the take we used in the movie. We didn't add any sound to that or anything," Rogen added, noting that Cera 'was concussed, I think.'

Rihanna didn't hold back when clocking Cera (Neil Mockford/GC Images)

Cera later spoke of the incident to GQ, saying:

“Yeah, I mean she definitely hit me, but I really, I wanted that, you know?

“I mean, I think it's a lot funnier and a lot more convincing… a fake slap just doesn’t look good.

"She really sent me flying, and it was great. And now it's on film forever, this pain that I experienced.”

Anyone who has seen the movie will know that this is just one of many, many strange moments in the post-apocalyptic film, with the Backstreet Boys appearing in heaven, Channing Tatum playing someone's sex slave and Jonah Hill getting possessed by a demon.

But now that I know that slap from Rihanna was real, Cera's brief cameo must go down as literally, the hardest-hitting moment of the movie.