Defending her appearance, the 21-year-old told PEOPLE, "Hollywood is all about the way you look, and I don't think that's the healthy thing for anyone. But, if you're strong and comfortable with yourself, then you're going to be fine."
On Tuesday she addressed the rumors again, saying she was surprised by the suggestion that she had an eating disorder. "(The press) said to me yesterday 'How does it feel to be called anorexic?' and I had no idea that I was," Knightley told the Associated Press. "I'm not saying there aren't people in the film industry that suffer from it, because I am sure that there are. But I'm quite sure I don't have it."
The questions about her health came up at the premiere when Knightley showed off her rail thin figure in a low-cut, backless bronze Gucci dress.
Still, she said there's nothing to worry about. "I've got a lot of experience with anorexia ? my grandmother and great-grandmother suffered from it, and I had a lot of friends at school who suffered from it," Knightley said. "I know it's not something to be taken lightly and I don't."
Adorned in vintage Cartier jewelry, Knightley said at the London premiere that was happy to be back in her hometown. "We had such a good response in the U.S., but I'm a London girl ? so it's always special to do a premiere here," she told PEOPLE.
For his part, Pirates star Johnny Depp was decked out in a fedora and sunglasses to keep his cool in the uncharacteristically hot London. He greeted fans and signed autographs for more than an hour.
Costar Orlando Bloom was also at the Pirates premiere. Press reports say he couldn't help himself, and peeked down the front of Knightley's gown, which opened to her belly button. "I haven't flashed anyone yet," she joked.
Among the other stars sighted: singer Charlotte Church, dealing with the heat in a white sundress and flip-flops, and Mischa Barton, sporting a blue baby-doll dress.