This weekend, Michael Douglas is due at the Deauville Film Festival in France, where he first met Catherine Zeta Jones many years ago. Poignantly, this visit comes as the couple announce, after frenzied speculation, that they are separating, to "evaluate and work on their marriage". Whether divorce will follow isn't certain. But the timing of the separation coincides rather neatly with Douglas's memorable comments about the contracting and curing of throat cancer.
"This particular cancer is caused by HPV [human papillomavirus], which actually comes about from cunnilingus. . . it's a sexually transmitted disease that causes cancer. And if you have it, cunnilingus is also the best cure for it." That was Douglas's eye-popping remark back in June. Only later did he think to clarify that his wife had nothing whatsoever to do with it – via the medium of Barbara Walters, who told her millions of viewers: "Michael would like everyone to know that his wife, Catherine, is healthy. She does not have the HPV virus. He doesn't know how he got cancer. He does not want anyone to think it was from Catherine."
After everything they had been through together – the cancer itself, the treatment, Catherine's bi-polar diagnosis, and Douglas's son Cameron's incarceration for drugs – this was apparently a bridge too far.
Back in 1998, Douglas's first words to Catherine were: "I want to father your children." She may well not have been the first woman to whom he uttered those words, but in this case, at least, they were prophetic.
She became his second wife, and they went on to have two children, Dylan and Carys, and amass a fortune. Back then, she was a rising star, having begun to move from the world of TV into feature films, with The Mask of Zorro, while he was already an established movie icon, part of 'old Hollywood', thanks to his father Kirk.
She was then in her late 20s, but with the kind of glamour and serene beauty that made her seem older. She also pulled off marrying a man 25 years her senior – they share a birthday – an elder statesman in an industry she was just beginning to crack, without appearing ridiculous.
Despite the age and celebrity-gap, the marriage seemed stable and affectionate. When the usually thorny issue of a prenuptial agreement reared its head before the wedding, Zeta Jones simply took it in her stride.
"I think prenups are brilliant," she told Vanity Fair in 2000, just months after getting married. "It wasn't a nasty experience for me," she continued. "It was like 'Thank God that's done. . . let's get on with it.'" And get on with it they did.
Both continued to make successful films, Catherine fulfilling all her early promise and starring in Traffic and America's Sweethearts, and then Chicago, for which she won a Best Supporting Actress Oscar in 2002, while Douglas made Wall Street: Money Never Sleeps, and recently, Behind the Candelabra, one of the best films of his career.
The dynamic of the relationship seemed steady and thoughtful – he was the wise-cracking, good-time guy; she the stately but grounded beauty from the Welsh valleys. Having earlier admitted to addiction problems – he checked himself into rehab shortly after making Basic Instinct, apparently for alcohol and drugs, although the one that really caught the headlines was, of course, sex – Douglas seemed more than content to settle into a life of golf, movie-making and fatherly duties.
However, Douglas, despite admitting to problems, later maintained that he was not on a path to total oblivion: "Despite all the information one accumulates, and despite the damage you know smoking wreaks on people, they still do it. It's the same with alcohol. Drinking has nothing to do with highs, thrills, whatever. It has to do with many other causes. I'm not self-destructive. . . where did that sex-addiction stuff come from?"
In 2010, the couple apparently renewed their vows, and almost immediately afterwards Douglas was diagnosed with stage IV throat cancer, whereupon he underwent aggressive treatment.
The couple largely retired from public life for the duration. Although the outcome has been a happy one, it seems to have triggered an episode of bi-polar II disorder for Zeta Jones. This is a disorder of the neurotransmitters in the brain, and while bi-polar II is less serious than bi-polar I, accompanied by less severe highs and lows, it is still an immensely difficult condition that requires careful management.
The exact causes are unknown, although hereditary factors play a part, but very often, it is triggered by particular events – a brush with death, alcohol or drug abuse, post-natal hormonal changes, ongoing intolerable stress for example.
Catherine Zeta Jones has experienced episodes of the disorder before, and has publicly said that she intermittently needs professional care to keep her condition in check. In a world where mental illness of any kind is treated with suspicion, her admission was very brave: "If my revelation of having bipolar II has encouraged one person to seek help, then it is worth it. There is no need to suffer silently and there is no shame in seeking help," she said at the time. It also sheds light on the on-going troubles the couple have faced in recent years.
Not least of these has been Douglas's son Cameron, from his first marriage, who has battled addiction for years, and was arrested in 2010 for dealing crystal meth and cocaine from a hotel room in New York. Since then he has been jailed, and further drug infractions in jail led to his initial sentence being almost doubled. Douglas, naturally, carries the guilt of the divorced father and is consumed by his frustrated desire to help, whereas Zeta Jones is without the same blood ties.
Finally, underlying all the many difficulties and challenges the couple have faced together, is the relentless ticking of time, and the kind of psychological widening of the already considerable age-gap between them that inevitably occurs. When they met, she was 29, he was 54, both were in their prime. It's a picture that looks rather different now, when he is 68 and she is 43, confronting what is probably the most difficult decade for women, especially beautiful women whose looks are their currency.
These are the years when the subtle indicators of age are laid down, despite the best efforts of expensive creams and dermatologists.
The ultimate futility of resistance is made clear and, given Hollywood's previous track record, a steady dwindling of decent roles spell out mortality in garish terms. Zeta Jones isn't a mesmerising actress, her appeal is skin-deep, and that has been enough. Until now.
In an interview just last month, Douglas said: "True love takes work. Love is an extraordinary feeling that comes from the bottom of your soul, but has to be nurtured, you know. The thing I've learned about getting older is you can't take love for granted. You protect it, nurture it and it grows and after one's initial, physical, emotional aspects, it becomes deeper."
Whether he will have a chance to prove that now, is very uncertain.