She's known for her willowy, super svelte frame and is regularly spotted heading to the gym to work-out.
But Kristen Stewart has ditched the healthy diet for her latest film as she's been gaining weight to get into the role.
An on-set source told omg! that the A-lister has been asked to put on a few extra pounds by director Olivier Assayas for her part in new movie Sils Maria - as he didn't want her to look like a trim and toned Hollywood starlet.
The source confirms that the acclaimed director wants Kristen to look ''dowdy and puffy'' for the film, in which she plays an assistant and confidante to Juliette Binoche.
In order to bulk up her slimline figure, Olivier has put her on a daily diet of more calories than usual to make sure that she achieves the figure that he wants.
The insider adds that Kristen has been munching on chocolate squares throughout the day in between takes in a bid to gain the weight. Okay, now we're really jealous!
To add to the image overhaul, the Twilight star has also had her trademark dark hair dyed a shade of auburn to get into character.
But while some more image-conscious actresses may hate having to make themselves more dowdy, it seems that Kristen has been relishing the opportunity.
Our source tells us that the star loves her new hair colour so much that she's going to be keeping it after filming, and that she's quite enjoying not being so skinny. Good for you, Kristen!
The actress recently spoke to WWD about the role, saying: ''I play a personal assistant to an actress.
''It takes two very particular people to have that relationship be functional - one that services the other - because Juliette Binoche is playing the actress that I assist, and she is one of the most powerful women I think I’ve ever seen in film.''