The Twilight actress appeared on The Tonight Show with Jay Leno last Thursday, where she revealed that she accidentally punched the Thor star in the face.
"It made such a sound," Stewart told Leno. "It was in a scene. Girls, if you've ever wondered if it works, it works! It literally spun him right around! I was supposed to miss him."
The actress went on to insist that she wasn't pleased with herself.
"I'm not proud though," Stewart said. "Instantly, tears sprung to my eyes. Like, 'Ahh, are you okay?' But it will definitely be in the movie."
The actress added that her punch left Hemsworth with a black eye "and a big lump on his nose".
Stewart recently revealed that she is not bothered by rumours about her that appear in the media.
Last month, the actress was reportedly injured herself on the set of the fairytale film, shutting down production for a few days.