Keira's revealing evening dress shows there's even less of her than we thought

And she didn't choose an evening dress to cover the shrinking frame that created as many headlines at the annual festival as the film in which she stars.

It was more revealing than ever - the silver-grey Rodarte dress was slashed across her chest.

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Keira's dress was slashed to reveal her chest

Even the gathered layers of the dress couldn't hide Keira's skinny profile

Viewed from behind, you could be forgiven for thinking she had got tangled up in her bedsheets.

But this was Keira adopting the look of a Greek goddess.

No one could accuse the 22-year-old actress of not making an effort as she arrived on the red carpet in the floor-length robe, complete with diamond-encrusted Bvlgari tiara and Chanel ring.

Draped loosely over her shoulder, the dress did nothing to disguise her highly slender frame.

She was also happy to show off most of her front, which she has always been brutally honest about.

The actress, currently dating actor Rupert Friend who also attended the premiere, has previously spoken of her dislike of her chest, saying: "I don't have any t*** so I can't show cleavage."

Keira, who delighted fans in Leicester Square by signing autographs and posing for photographs, has won rave reviews for her role in Atonement, an adaptation of the wartime Ian McEwan novel

She plays Cecilia Tallis, an upper class beauty whose fledgling love affair with the housekeeper's son, played by James McAvoy, is destroyed by a tragic misunderstanding.

Directed by Joe Wright, Atonement is being hailed as one of the strongest British films in years and is widely tipped for an Oscar.

But Miss Knightley played down the chances of it - or her - winning the coveted award.

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The Rodarte dress was a confection of gathers, swags and knots

She said: "The fact that the film is in the same sentence as the word Oscars means we've done a good job already. "If it doesn't get a nomination, it doesn't take away from how proud I am."

Last night's appearance will have done nothing to shrug off the constant comments about her gaunt look.

But she is sure that the critics will be overwhelmed by the film. "I knew it was quite good when my mum went to see it and was crying."

Keira and co-star James McAvoy are all smiles at the London premiere of their film, Atonement