'There are some friends," intones Stephen Fry at the beginning of the semi-autobiographical 1992 film Peter's Friends, starring, among others, Emma Thompson and Kenneth Branagh, "you know you will have for the rest of your life. You're welded together by love, trust, respect, loss or – in our case – embarrassment."
Oh dear. While, two decades on, Fry still commands awe as a polymath and actor, clearly his fortune-telling skills weren't up to much. Within three years, Thompson and Branagh, who were at the time the golden couple of British acting and whose performances are two of the film's star turns, had announced that they were separating. And until now, no one had really confirmed why.
In a world of reality TV, celebrity magazines, Twitter break-ups and make-ups, it's hard to think back 18 years, and to the relative silence that accompanied the Branagh-Thompson split.
At the time, they were two of the biggest names in Britain. Known simply as "Ken and Em", their relationship invited comparisons with the glamour of Laurence Olivier and Vivien Leigh. Yet despite whispers of Branagh's "private and complicated" relationship with fellow Brit actor Helena Bonham Carter, and Thompson's subsequent relationship with (her now husband) Greg Wise, no one was any the wiser.
But this week Thompson has finally lifted the lid on what happened with charm and self-deprecation. "[It] is, as Mike Nichols [the director] once said . . . all blood under the bridge. You can't hold on to anything like that," Thompson said. "She's a wonderful woman, Helena."
Thompson and Branagh had met in 1987 when they appeared in a mini-series, Fortunes of War. Belfast-born Branagh was a former comprehensive pupil; Thompson was part of a theatrical dynasty (her mother, Phyllida Law, was a classical actress; her father, Eric, wrote and narrated The Magic Roundabout).
Two years after meeting, they married in a lavish ceremony. They carried on their union into their professional lives.
Even after Thompson was described by the New York Times as an "international success almost overnight" for her role in Howards End (for which she won an Oscar for Best Actress in 1993, and in which Bonham Carter also starred, as Thompson's sister), she returned to acting with Branagh in Much Ado About Nothing.
But cracks were forming. As his wife's star was rising, Branagh was struggling to make a success of his first big-budget film, Mary Shelley's Frankenstein, in which he played Frankenstein and Bonham Carter his fiancée and adoptive sister. It seems that the Ken and Em show was already in trouble – competing schedules, too much time away from each other – even before the affair with Bonham Carter, which is believed to have started on the Frankenstein set in 1994.
And yet the split would prove a miracle for Thompson's professional and private life, transforming her from London luvvie to UK national treasure.
On set, she also found a new husband in the handsome Greg Wise; nearly 20 years later they are still going strong.
Bonham Carter is in a long-term relationship with Tim Burton, while Branagh married Lindsay Brunnock, an art director, in 2003.
Now, she can even joke about it. Asked whether the situation had not been tricky because the two actresses seem quite similar, she replied: "Oh we are. Being slightly mad and a bit fashion-challenged. Perhaps that's why Ken loved us both . . . Helena and I made our peace years and years ago."
Of course, for most mortals, waiting 18 years to say anything about the break-up of a marriage – and then being generous about it – seems an impossible challenge.
Who can blame Jennifer Aniston for taking to Vanity Fair and US Vogue to make clear her hurt and betrayal after Brad Pitt left her for Angelina Jolie? (Aniston lambasted her former husband as lacking a "sensitivity chip").
Jo Wood was humiliated by her Rolling Stone husband Ronnie – keeping him sober only to see him start a relationship with a 19-year-old when he was in his sixties – and promptly sold her story about him spending the kids' school fees on a Rolex.
But however delicious revenge might seem at the time, who suffers in the end?
The problem is that you end up being forever linked to the ex you grew to loathe. It can even damage your professional life – French president François Hollande's credibility has not fully recovered since late last year, when he found himself in the middle of a furious row on Twitter (where else?) between his partner Valérie Trierweiler and his ex, Ségolène Royal.
While for most it would be unthinkable to utter the words "wonderful woman" for the Other Woman, for those who can't face the Thompson decision to button it, think only of these two words: Vicky Pryce.
Her attempts to seek revenge on her husband Chris Huhne and his new lover Carina Trimingham ended up with both Pryce and Huhne disgraced and in prison.
Now that sounds like the beginning of an Oscar-winning screenplay – eh, Emma?