“I don’t analyse my way of thinking,” Lagerfeld tells a phalanx of journalists after the show in response to a question about whether he’s taking a more cinematic approach to his work. “But it’s a good motivation.”

Stewart, who stars as a grumpy starlet (perhaps a cheeky reference to her real-life persona), says she feels “blessed to be part of something that isn’t just contrived and money-driven”.

It’s been said by more than a few fashion insiders that the industry should be more cinematic, and Once and Forever, a fictional behind-the-scenes look at the making of a Coco Chanel biopic, is as much about cinema as fashion gets.

The dreamworld of fiction is a powerful evocation of style, and much more potent than standard runway shows, which have become heavily merchandised.

Perhaps more than anyone in the industry, Lagerfeld knows this – over the years his Chanel shows in Paris have transformed the Grand Palais into an airport; a tropical, origami-inspired paradise, and even a kitsch supermarket. Now he’s doing several short films for Chanel starring Hollywood starlets and catwalk queens.

In Rome, models such as Lara Stone and Freja Beha emerged from a Metro station on a catwalk designed to look like a Parisian street, all in black and white to reference art-house films. Hair piled up high, eyes slicked with thick kohl and wearing sexy dresses, skirtsand lace slashes, it showed a highly sensual and provocative side of Chanel, something that we don’t see often.

The muses? It was full of references to Italian screen icons and French actresses of the ’50s and ’60s who, often dressed in Chanel, became darlings of Italian cinema. There was Romy Schneider post-Sissi in all her womanly glory. Stone played a convincing Anita Ekberg from La Dolce Vita.

“Lara’s great, there’s no one who could play her that well,” Lagerfeld says.

There were touches of Les Enfant des Paradis (Children of Paradise) by Marcel Carne, which Lagerfeld calls his “favourite French movie”. He plays on a romantic idea of Paris, which might be the last thing on people’s minds after the recent terror attacks.

“The atmosphere is not very good now in Paris. There’s not a lot of romantics left, so we’ll have to work on that.”

Modern tweed suits, leather caban coats and slip dresses were paired with pointy heels and lace-up tweed hiking boots. There was ’60s glamour in the little capes, sometimes embellished or lined with feathers and figure-hugging lurex. Wearable and sexy, the collection was a great teaser for the Chanel-clad VIP clients from around the world that made up the bulk of the audience.

It wasn’t just the clothes that mesmerised: there were plenty of celebrities as well. A stunning Zhou Xun was accompanied by Hong Kong photographer Wing Shya, Hollywood actress Rooney Mara looked striking and bird-like in her pale pink chiffon layers, while Stewart, her flowing dark hair pulled back tight, was the main attraction – apart from, of course, Karl.

“You feel the love here, you absolutely feel the compulsion,” says Stewart of being part of Chanel’s inner circle. “Karl doesn’t do what he does for any reason other than what’s intangibly inside him, and that needs to come out.”

Stewart, who stars in Chanel campaigns, manages to balance being the make-up free, baseball-cap-loving tomboy of Twilight fame, with the ability to transform into serious fashion fodder courted by the biggest brands on the red carpet. In person, she is smaller and more fragile looking than on screen, but with the same ethereal elfin beauty, huge haunted eyes and deadpan stare (a look that defines “resting b*tch face”). Perhaps she’s the kind of unexpected Hollywood star that the eccentric Mademoiselle Coco Chanel might have approved of. The tomboyishness is something that certainly relates.

“My favourite kind of fashion always tells a story, and is always able to stir something in you that you didn’t know was there,” Stewart says. “And making the movie with Karl … I was not surprised that it was natural to him, it was an impulsive, spontaneous endeavour that came very much off the cuff.

“My favourite kind of cinema is the kind that takes risks and is not so planned, so his drive and his interest coincided with mine. It was wonderful.”