The movie's director Tom Hooper decided against using scissors as he wanted it to look more authentic by having her hair cut off with a knife for her role of Fantine in the movie musical, reported Contactmusic.
Actress Nicola Sloane was given the task of cutting Hathaway's locks.
"The director said 'I want it to look really vicious we need you to be hacking at it with a knife'. We blu-tacked a razor blade against a knife blade and I held the two together and you have to saw away at it that's the only way to get it off.
"She was all right and I had cut all the front and this little voice went 'cut'. I thought 'oh she's had enough' so I moved my hands away and then she burst into tears when she felt how short it was at the front," Sloane said.
She said Hathaway was very passionate about growing her hais long.
"She had been growing her hair for three years. Then I hacked it all off and made her look terrible," she added.
Hathaway, 30, later sold her hair in order to raise money for charity.
