Months of being sewn in to 18th century corsets have clearly taken their toll on Keira Knightley.

The 23-year-old Pirates of the Caribbean star arrives to meet eager journalists in what looks like a full-length frilly black nightie.

After portraying infamous 18th century socialite Georgiana, Duchess of Devonshire, in her latest film The Duchess, she is clearly taking full advantage of the modern right to breathe.

"The costumes were fantastic because Georgiana was a famous fashion icon. But they weren't particularly comfortable," she says.

"In a corset you can't catch your breath. It means your emotions are heightened because you can't calm down."

Considering she plays an aristocrat whose glamorous, yet tragic life has led her to be compared with the late Princess of Wales, this was not such a bad thing.

Author Amanda Foreman is largely responsible for bringing the duchess's life back into the spotlight, thanks to a biography she wrote in 1998.

Details about her husband's infidelity, her trend-setting outfits, affair with the future Prime Minister Lord Grey and eventual menage à trois with her husband and former best friend Lady Bess Foster, proved sensational reading and was an instant hit.

The film version, released today, stars Knightley along with Ralph Fiennes as the Duke, Dominic Cooper (The History Boys and Mamma Mia!) as her lover Lord Grey and Hayley Atwell (The Line of Beauty) as Bess.

Although the film's producers are hoping that linking Diana, Princess of Wales with her great-great-great-great-aunt Georgiana will help to attract audiences, Knightley says she didn't play on the connection.

"I was 11 when Diana died. I knew when I was going into it that she was a distant relation but that's as far as my knowledge went. I was making a film about Georgiana Duchess of Devonshire and I think she's an interesting enough person to warrant a film about her, without comparison."

The beautiful and charismatic Georgiana was married at 17 to the Duke of Devonshire – a man more interested in sleeping with the maids and playing with his dogs than his new wife – and for many years was unable to bear him an heir.

Her husband ignored her as a result and her dreams of a fairytale life gradually died.

But despite her personal problems, the young duchess won the heart of English society and only the Duke seemed immune to her appeal.

"I first heard about the film when Saul (the director) sent me a letter with three really big ostrich feathers tied with a big bow," says Knightley. "They were very pretty and I thought 'I have to work with a man who does that'."

The feathers were a nod to one of Georgiana's more flamboyant head-dresses which helped to turn her into one of the most talked-about women of her time.

"When I read the script, the first thing that struck me was how incredibly lonely this woman was," says Knightley. "She was constantly surrounded by so many people and yet she was entirely alone. I think she just tried to grab on to any kind of love and attention that she could possibly get."

Naturally enthusiastic and intelligent, Georgiana became involved in politics and eventually fell in love with the future Prime Minister, Lord Grey.

But despite having to accept her husband's mistress in a humiliating and extremely public menage à trois, her love for Grey was forbidden by the Duke.

"The whole journey for her is one from idealism to reality – she gets broken down. She couldn't have lived with herself if she'd gone off with Grey and given up her kids. I don't know if it has a happy ending, but I think that she survives and that can only be positive."

Although the 18th century paparazzi at that time constituted of a bunch of talented cartoonists, as one of the most powerful, beautiful and controversial ladies in the land, the Duchess' life was still the subject of endless gossip and public speculation.

Like her modern-day equivalent, Princess Diana, the thrill-seeking aristocrat found it difficult to keep out of the headlines.

"The current Duchess of Devonshire showed me some of Georgiana's things. She was a huge gambling addict, so it was amazing to see her books of debts written in her own hand," Knightley says.

As well as her love of cards and extravagant shopping habits, the Duchess liked to socialise and drink with society's opinion makers.

The public adored her unique combination of intelligence and wilful self-destruction.

Knightley appears in almost every scene of the film and admits that playing the Duchess wasn't easy.

"It was terrifying. It's very rare to get a role like that, so when it comes along and you get the opportunity to play
it, it's phenomenal and terrifying."

Although she had a lot on her plate, Knightley did let her hair down occasionally during filming – but not literally, as the authentic 18th century headdresses needed to be painstakingly unpinned.

"During the sex scene with Grey I was luckily fully clothed but he got to wear a skin coloured nappy. On set, you're supposed to be supportive of each other but when he came out I completely lost it.

"I couldn't stop laughing and Saul did come over and say, 'Come on, pull yourself together and do some serious work'."

Shot over nine weeks in the autumn of 2007, the film is set in three principle locations, the Devonshire's London home, Devonshire House; their country estate, Chatsworth and Bath.

Several locations were used to recreate their lavish homes including Kedleston Hall in Derbyshire, Holkham Hall in Norfolk, Osterley Park, Somerset House in London and also Chatsworth, the ancestral home of the Devonshires, where the current Duke and Duchess still live.

"Being in those enormous houses helped with the feelings of isolation that I thought Georgina was
going through. The scale and beauty is quite astounding," she says.

But having played such a wonderful role does she hope more similar projects will come along?

"Recently I do seem to be getting sent books and
ideas for strong female characters, which is
fantastic. I think if people go and see films about strong women, they'll be more made and if they don't, they won't.

"It's up to the public."


Keira in her own words

"I wish I was Sienna Miller. She talks to everyone and laughs and smiles and looks as if she is genuinely enjoying herself. When I talk to her, I hope a bit of her party personality will rub off on me, but it never does."

"I'm not comfortable having to be myself, or being photographed as myself. Australian Aborigines say that with every photograph taken, a piece of your soul goes with it. And there are some days when I kind of believe that."

"Not going to university did give me an incredible driving force because it leaves you with a slight chip on your shoulder.

It makes me feel I am going to read absolutely everything so I can prove that I am not stupid."