Sienna Miller was shocked when she slimmed down for her role in upcoming movie FACTORY GIRL - because her boobs vanished.

The Alfie beauty - who will plays Andy Warhol's muse Edie Sedgwick in the film - was prompted to trim down when she discovered her character suffered from an eating disorder, but her love of fast food left her unable to match Sedgwick's figure.

She says, "I really wanted to lose weight when I found out Edie was anorexic. In the end, I didn't lose as much as I'd planned because I'll always be a hamburger-and-chips girl. I don't do fruit - just burgers. I eat loads and loads.

"One of the problems I found when I did lose weight was that something bizarre happened to my boobs. They've always been small, but now they've disappeared - they've just shrunk."