Watch her at the Toronto International Film Festival news conference for The Duchess - the elegant, engaging tale of the 18th-century aristo Georgiana, Duchess of Devonshire. When a reporter notes the similarities between this cloistered noble-gal whose family name was Spencer, and her 20th-century descendant Diana, Princess of Wales, Knightley beams brightly. Then she parries back the fact that she was all of 11 when Diana died.
"I'm afraid I'm very ignorant about Diana," Knightley explains later, in a suite at a nearby hotel. "My family weren't people that had any gossip in the house, so I wasn't - I know parts of the story, but not enough to be able to say yes, this is a parallel. . . . And I can definitely say that when we were making the film, none of us spoke about Diana at all. . . .
"Probably you can draw parallels to many different women. Marilyn Monroe keeps coming up a lot. And Josephine Bonaparte, in a way.
"However, I think the Duchess is interesting enough on her own not to need parallels."
And, OK, she is. As portrayed by Knightley in a succession of knockout gowns, befeathered and bejeweled, her head topped in towering coifs, Georgiana was a naive 17-year-old married off to William Cavendish, soon to be the fifth Duke of Devonshire. (And played with haughty relish, and tinged with melancholy, by Ralph Fiennes. Charlotte Rampling, stoic and stunning, is Georgiana's mother.)
The Duchess failed miserably at her one "job" - to provide the Duke with a male heir - instead giving birth to a gaggle of girls. Keen on politics, she was considered out of her depth - and anyway, what does a woman know of such things?
So she took to wearing outrageous, cutting-edge couture. Not unlike the cover girl of the September Vogue - that would be the cheekboned, square-jawed Knightley - Georgiana was considered an icon of glamour, arbiter of high style.
Which leads us to another parallel: celebrityhood.
Back in 1770s London, the press stalked the Duchess, printing artful sketches of her likeness in the news dispatches of the day. In 2008 Toronto - where Knightley is doing interviews with a personal bodyguard outside the door - the press stalk the actress. Photos appear online in a matter of hours, in the tabloids the next day.
"I thought celebrity was a modern phenomenon!" she reflects. "And I think the scale of it is - the cell phone cameras, the Internet. . . . But I think it is interesting that it's been around for 300 years, and that we're still interested in the same things. We haven't really grown any. There you go."
Still, for Knightley, that's not what The Duchess - which will open Friday at the Ritz Five and Showcase at the Ritz Center/NJ - is about, either.
"It's the least interesting thing, really, about her," she explains. "For me, it was really simple, and there's no need to get psychoanalytic about it: She has this need for attention, and as soon as she's not getting it at home - where she's been such a huge failure, unable to produce an heir - she's trying to get strangers to love her."
"People who will approve of you simply because of the dress you're wearing, or whatever. And I thought that was quite an interesting part, that need for that much attention. I don't know" - and here Knightley laughs - "probably something like that was going on with me back then."
Knightley (who, by the way, is the face of Chanel Coco Mademoiselle fragrance) nails the performance. There are famous portraits of Georgiana by Gainsborough, among others, that show an uncanny physical resemblance between the 18th-century Duchess and her 21st-century portrayer. But Knightley brings a naturalism to her role, a brightness, that adds poignancy to this prisoner-in-a-gilded-cage tale. To see her Georgiana brutalized and broken is a heartbreaking thing.
Knightley is the product of a London family - father Will Knightley, an actor, and mother Sharman Macdonald, a writer - where art and politics were the stuff of dinner-table conversation. Even now, the actress chimes in about how her mother is reading the autobiography of Juliette Grco - the French resistance fighter/chanteuse/bohemian muse.
"My mum's reading about her, in French. And she keeps on trying to talk to me in French about existentialism. Now, I have schoolgirl French, so it's quite a one-sided conversation."
Saul Dibb, the British director who hired Knightley for the title role in The Duchess, says the young woman with the schoolgirl French turned out to be everything he hoped for - and more.
"With Charlotte Rampling to one side and Ralph to the other, I just felt Keira held her own against two of Britain's best and most experienced actors," Dibb said in a separate interview. "She was the measure of them, as her character was the measure of theirs."
Knightley seems to pop up with a new film every year in Toronto: Last September it was Atonement, in which she played the upper-crust love interest to James McAvoy's tragically fated servant-turned-soldier. In 2005, Knightley was here with Joe Wright's version of Pride & Prejudice. She was Lizzie Bennet, and nominated for an Oscar for the work. In and around such classy fare, she's managed to do three blockbuster Pirates of the Caribbean with guys named Depp and Bloom. And a few weeks before starting on The Duchess (which may well bring her another Academy Award nomination), she wrapped The Edge of Love, in which she plays Vera Phillips, lover of Welsh poet Dylan Thomas. He's portrayed by Matthew Rhys. Sienna Miller and Cillian Murphy also star.
Although her name's been linked to several projects (a new King Lear, for one), Knightley claims to be on the loose, "free and floating," without a job. And happy about it.
"I don't like the idea of being booked up," she says. "I hate the idea that you had so many films that you knew exactly what you were going to do two years in advance. That would make me very depressed. . . .
"For me, I have to do what interests me at that moment, it has to be something that I can get completely obsessed with, otherwise I think the performance would be - "
Yes? Would be . . . ?
Knightley just stops. She's flashing that smile again, swatting the conversation to a close with a blithe but determined shrug.
Contact movie critic Steven Rea at 215-854-5629 or firstname.lastname@example.org. Read his blog, "On Movies Online," at http://go.philly.com/onmovies.
Opening Friday at the Ritz Five and Showcase at the Ritz Center/NJ