In the upcoming adaptation of the hit stage show, Hathaway plays Fantine, an impoverished mother who is forced to chop and sell her long locks to provide for her daughter.
Now Jackman, who stars as Jean Valjean, reveals Hathaway was so devoted to nailing the emotional scene, she brought her own hairstylist to the shoot and asked him to slice her head open as they filmed.
He explains, "They were in the make-up trailer discussing how they were going to do it because they had to cut it live on camera and she said, 'If you cut my head while you are doing it that would be great - to get the blood in the scene.'
"(The stylist) had to wear a dress to pretend to be a woman. You don't see his face, but if you look closely you can see these man hands holding the scissors."
Hathaway previously admitted she broke down in tears after her Les Miserables makeover, insisting, "I wasn't expecting it to be such a big deal because it was my idea. It's something I've wanted to do for such a long time and I knew it was something that the character did, so I offered it to the director and he said yes. Then, as it got closer, I just thought, 'Oh, well, I can't really take it back now.'
"I've done back flips out of windows, I've jumped off of buildings and yet cutting my hair reduced me to, like, mental-patient-level crying. I was inconsolable."