“Maggie is a mystery,” he says, finally. “I don’t know if I ever fully understood her. I thought I did, but she’s even more of a mystery to herself.”

Cheung is the star of Assayas’s latest film, Clean, about a faded, drug-addicted pop star trying to revive her career and her health in order to regain custody of her young son. The role won Cheung the Best Actress prize at Cannes last year and reunited her professionally with Assayas (pictured) who gave the Asian star her first Western cinema part in his 1996 film Irma Vep.

The actress and her director became a golden couple of international arthouse and married in 1998, he the darling of new French intellectual cinema, she the enigma of trendy Wong Kar Wai films, a style icon and Hong Kong national treasure. Their divorce came through while they were together, on set, filming Clean.

“I wrote the film for Maggie,” Assayas says. “When we separated two years before, I tried to see it with other actresses in the part but I couldn’t. Nothing was making sense without her. And she didn’t want to let the part go. She was inspired by it.” Assayas has never publicly spoken about their break-up before, preferring to concentrate on the thematic and intellectual side of his work. His nervy pauses suggest that he’s articulating these thoughts for the first time.

“We both seemed to be pushing each other to make it and I think we both thought making the film would be good for us on a psychological level, that we might get some closure from it.”

And did they? “No,” he says with a rueful laugh. “Not immediately, anyway. Although now, after the film’s release into the world, I’m starting to think it has helped. I tend to look for meaning in life and, you know, we made this film, she won at Cannes, we’re not together any more but we’ll always have this film. So the marriage wasn’t an absolute waste. It was a partial disaster, not a total one. That is how I have come to reconcile myself with things now.”

Assayas and Cheung will be reunited briefly in London tomorrow evening at a preview screening of Clean as part of the Renault French Film season. It must be hard, emotionally, I suggest, no matter how amicable things are, to watch, praise and admire her.

“Maggie is a fantastic actress,” he says. “That is what first drew me to her and we were very good on set together, working professionally. When I looked at her through the lens, it was professional not emotional. I was the director and she was my actress, even though she was also very much a driving force for the film. I seem to be able to make a separation between the practical reality and the emotion.

“But when we were married, things were off balance. We didn’t spend enough time together. I couldn’t work in Hong Kong and she couldn’t be in Paris too long. Maggie’s a conflicted individual, always wanting to be somewhere else. She’s so many things that she’s forgotten who she is.”

Cheung — probably best known here for In the Mood for Love — brings that lost, ethereal quality to her performance in Clean as she travels from Canada to London and Paris, looking for support from family and old friends who have long given up on her. For Assayas, the film expands upon the notions of modern love he first chronicled in his 1998 Parisian ensemble piece Late August, Early September.

Clean, a haunting, mournful film, is partly about seeing things clearly again, so it’s a poignant irony that its director, as we talk at the recent Bangkok Film Festival, can now assess it on a personal level as well as an intellectual one, acknowledging how its themes are in accordance with his developing world view.

“When I was with Maggie I spent much time being lonely and writing in Asia,” he reflects. “I saw cities like Tokyo, Bangkok and Hong Kong changing into the future in front of my own eyes. In Asia, you feel like you’re five minutes ahead of the rest of the world.”

This “globalisation” had a surprisingly profound effect on Assayas, formerly a Cahiers du Cinéma critic and a great student of classical French literature. After the lengthy 19th-century costume drama Les Destinées Sentimentales, with Emanuelle Béart, his next film, Demonlover, featured a flashy international cast (including Chloë Sevigny, Connie Nielsen and Gina Gershon), ultra-modern corporations and global internet espionage. It was widely derided but has built up a cult following for its post-apocalyptic atmosphere and striking, futuristic design.

“We used to live in a world of many different ideologies and philosophies,” he explains. “Now there’s just commerce, which rules everything, everywhere. Art has to be driven by some kind of anger and I discovered mine has to do with the way people just witness the world and let it happen around them.”

Assayas is a youthful-looking 50-year-old who grew up steeped in French cinema. His father was Jacques Rémy, a scriptwriter who worked with directors such as René Clair and Henri Clouzot. “It wasn’t at all glamorous though,” he recalls. “They were a rather old, serious and unattractive lot, actually. They were those whom the Nouvelle Vague were reacting against, but it was a difficult period for French culture because of the moral mistakes many artists had made collaborating with the Germans in the Second World War. I remember the tension between authority and rebellion of that period and that is still an influence on me.”

Unusually for a young(ish) film-maker, Assayas cites literature rather than cinema as his artistic inspiration, with Proust, Baudelaire and, particularly, Racine as his idols. “Before I start writing my films, Racine’s the one writer I often re-read. I’m fascinated by the tension between the strict classical form and the experimentation and depth within the verses.”

There is certainly something of the tragic Racinian heroine about Maggie Cheung’s character in Clean, tortured by society’s rules and morality judgments.

Assayas agrees. “That’s the battle. I try to make films that don’t play by the rules,” he says. “It’s the one, tiny political act I can have a grasp on in the modern world. I find controlling other things like love much harder.”

• The Renault French Film Season (0871 2002000), Glasgow, Edinburgh and London, March 30 to April 1

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