Actresses Keira Knightley (L) and Sienna Miller stand together on the red carpet before the premiere for their new film 'The Edge of Love' in Edinburgh, Scotland on June 18, 2008.[Agencies]

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Keira Knightley has reportedly banned studio bosses from digitally enhancing her cleavage.

The 23-year-old actress - who plays Georgiana, the Duchess of Devonshire, in period drama 'The Duchess' - is "proud" of her modest assets and didn't want them changed in any publicity shots.

A source said: "She has insisted that her figure stay in its natural state. She is proud of her body and doesn't want it altered. "But she looks flat-chested throughout the whole movie."

Keira's decision comes after her breasts were enlarged for posters and in publicity stills for her 2004 movie 'King Arthur'. She said at the time: "Those things certainly weren't mine! I was like, 'OK, fine. I honestly don't give a s**t!' "

Keira - who is dating her 'Pride and Prejudice' co-star Rupert Friend - previously revealed she would like to have larger breasts, adding: "I would love to have boobs! I'm never going to get them. I'm naturally who I am."