They were always meant to stay together, even though they never married. They had love, children and were soul-mates at home - and very often on the silver screen too.
Even more famously, perhaps, they breathed the same air politically. (And it wasn't Republican.) That was Tim Robbins and Susan Sarandon, Hollywood's golden couple whose lasting affections stood against the prevailing wind of acrimonious movie star break-ups.
But something went wrong. They kept it a secret for months, but the news got out this week, in a statement from Sarandon's press people which was as clear as it was short on detail. It said: "Actress Susan Sarandon and her partner of 23 years, actor Tim Robbins, have announced that they separated over the summer."
If gossip magazines will struggle to identify what sundered them, filmgoers may be more concerned about what it will mean for the celluloid arts. Few modern La-La-land pairings have been as fruitful professionally than that of Robbins and Sarandon.
While they have made many films separately, their list of collaborations is impressive. Think, for instance, of the 1995 film Dead Man Walking, with Robbins directing and Sarandon winning an Oscar for her portrayal of real-life New Orleans nun and anti-death penalty campaigner Sister Helen Prejean. Or the acclaimed drama of 1930s unions, Cradle Will Rock , or the equally political Bob Roberts. It was, indeed, on a film set that they first met – Bull Durham, a baseball drama with Kevin Costner made back in 1988. Today, the couple, who lived mostly in New York, have two sons, Jack, 20, and Miles, 17, who grew up alongside Ms Sarandon's daughter, Eva, 24, from an earlier relationship.
If most Hollywood breakups are met with a roll of the eyes, this split will come as a genuine shock to fans who had come to view it as a rare exception to the disposable nature of movie-star marriages, an unbreakable bond that could survive the huge pressures that international fame brings to a relationship.
Blog sites were filled yesterday with comments. "Susan Sarandon and Tim Robbins have split up. Has the world come to an end?" one post read. Asked a few years ago why she and Robbins never married, Sarandon told Time magazine: "He is a guy guy and he is also 12 years younger than me. I won't marry because I am too afraid of taking him for granted or him taking me for granted – maybe it will be a good excuse for a party when I am 80."
That party will now, sad to say, be as surprising as it once seemed inevitable.