Charlize Theron on location on Hollywood Boulevard filming an explosive scene for her new movie 'Hancock'. Los Angeles, California - 11.09.07

The pair star in the forthcoming superhero film and one scene required Smith to raise his hand to Theron and despite practicing a "fake slap", the actor smacked her across the face for real.

And Theron insists it really did happen - despite denials from Smith.

She says, "He tried to fake slap me one time, but the fake one just didn't happen. We're still debating this one. I think he just hit me!

"But Will claims I leaned into his hand and that's how it happened. I was so shocked! I was like, 'He just slapped me!'

"But he said, 'I did not slap you. I had my hand there and you turned into it.'"

But Theron insists the incident didn't sour their relationship, she adds, "We're just like kids, it's so much fun. He's not a woman beater!"

Source: WENN