She was forced to lose weight to play the role of dying prostitute Fantine in the movie adaptation of Les Miserables.
And today the actress revealed the results of her strict eating regime while relaxing in Miami.
The 29-year-old slipped her slender frame into a black bikini for a trip to the beach with her mother Kate.
Beach break: Anne Hathaway soaked up the sun in Miami yesterday
Slender: The star has lost weight for her role in Les Miserables
Anne is in the city for Italian designer Valentino's 80th birthday.
She appeared self-conscious of her whittled down shape, quickly covering up in a grey T-shirt after emerging from the water.
It is believed that Anne has lost around 16lbs in just three weeks before filming began in London last month.
She is rumoured to have consumed just 500 calories a day - significantly less than the recommended daily allowance of 2,000 calories a day.
Self-conscious? The star quickly covered up in a grey T-shirt
Hat-trick: Anne alternated between black and white headgear
She also cut her once-lustrous long brown hair into a blunt crop for the part.
The star certainly appears more curvaceous in the upcoming film The Dark Knight Rises, which will be released later this year.
Anne will tackle the formidable Catwoman character in the forthcoming Christopher Nolan-directed movie.
Time to dry off: The star was still soaked as she headed back to her hotel
She recently received the seal of approval from former Catwoman, Michelle Pfiefer, who told Empire magazine: 'I think she's great. I'm actually very much looking forward to seeing her in that role.
'I'm a big fan of hers and I think she has everything you need for that role. She has the humour, she can go to dark places, she's obviously very talented. I think she's going to be really good.'
Although Michelle loved playing Catwoman in the Tim Burton directed movie, she isn't protective over the role.
Doting parent: The star's mother Kate was spotted combing Anne's short crop
Ready for fun and sun: Anne, pictured at the airport with her mother, is in the city for Italian designer Valentino's 80th birthday
She said: 'Halle Berry did it already, it's fine. The whole thing with Batman is that they're always changing the world with each director.
'I would have loved to have done it but I know that's not what the franchise is really about now.'
Michelle is a huge fan of Nolan's take on the franchise saying, 'I love it. It's very different to Tim's but I'm a fan.'
Transformation: Anne on the London set of Les Miserables in London last month and right, as Catwoman in the upcoming film The Dark Knight Rises
