At the Vanity Fair Oscars night party in the Sunset Tower Hotel, the scene was pure Hollywood.
In every corner, a genuine star sipped champagne. Meryl Streep, Daniel Craig and Penelope Cruz were there, squeezed up against the walnut-panelled walls by the throng. So, too, were Sir Elton John and Rupert Murdoch.
There was also Madonna, escorted by her exotic-looking toyboy Jesus Luz, and Sean Penn, who had just won an Oscar - his second - for Milk, in which he plays Harvey Milk, America's first openly gay man elected to public office.
Love and hate: Sean Penn and Madonna in the film Shanghai Surprise, in which the couple were often fighting
Now it is traditional for the winners of an Oscar to hold court at this event. Receiving lines form around the guests who are holding a gold statuette and the social etiquette is for elaborate graciousness on both sides.
But Penn is not much of one for doing the right thing socially. So, instead of accepting Madonna's congratulations, he gestured at the singer's new young lover and said: 'Thanks. Another kid already?'
This seems to have been Penn's idea of a joke, but it could not have been better designed to humiliate his former wife, who was been globally criticised for adopting Malawian boy David Banda.
Penn and Madonna married in 1985, and the jibe was exactly the kind of low verbal blow which Madonna endured during their toxic four-year marriage. She has said that Penn all but destroyed her with his drinking, moods and taste for pornography.
Young love: Penn and Madonna married in 1985 after a short courtship
And then there was his constant criticism and violence. Once, he tied her to a chair and beat her. Another time, he hit her with a baseball bat. He threatened to shave her head. He chased her out of their hotel room.
Several times he promised to go to rehab or therapy, or to father a child with her, and she took him back.
It was the most passionate liaison. Madonna has said privately that the fireworks between them were unlike anything she's ever experienced, before or since, and that includes her romance with Warren Beatty.
Their love-making would go on for hours. Penn worshipped her, in an almost obsessive way.
Chemistry: Madonna and Penn met at the Oscars
And all these years later, the couple have an equally intriguing relationship as the best of enemies.
Each seems to remain unaccountably fascinated by the other, and a whiff of unfinished business hangs over their sporadic social contact. What is it about the 'Poison Penns' which draws them together? Can it really be true, as has been asserted, that Penn believes they are a latter-day Taylor and Burton, doomed always to love each other? The messiest marriage in Hollywood history was made in a flash of mutual attraction in February 1985.
Sean Penn happened to be on the movie lot when Madonna was filming her Material Girl video, and was intrigued by the singer.
She was just about to become a global superstar; he was minor Hollywood royalty, a Bratpack actor who promised to become something more.
He'd had a happy, middle-class childhood, going surfing and hanging out with neighbourhood pals including fellow actor Emilio Estevez.
But for all this, he liked to act rough-edged: drinking, swearing and riding motorbikes.
At 24, he was two years younger than Madonna, and they discovered that their birthdays were a day apart. They were instantly hooked on each other.
Madonna's brother Chris noted: 'He is a dead ringer for our father as a young man, and is middle class like Madonna, but with a street kid persona.
'He presents himself as a bad boy and a rebel - just like our brothers. It's patently a recipe for disaster.'
They were married that August, with Madonna at the peak of her early fame. Even by the time of the wedding, it was evident that this union was a colossal clash of egos.
Stormy: Madonna and with Penn in 1986, says he destroyed her with all his drinking, moods and addiction to pornography
Penn wanted an open-air ceremony and chose as the venue the Malibu home of friend Kurt Unger.
Madonna wanted to have an official photocall and would have been happy to pose in her strapless white wedding gown.
Penn insisted on privacy and became so enraged by the media helicopters hovering during their vows that once the five-minute ceremony was over, he returned to the house, came out with a gun and started shooting. It was the first of many tantrums over media attention.
Madonna, by all accounts, was screaming at him to stop being so crazy. 'What's the big deal, Sean?' she said. 'Leave them.' Guests, who included Andy Warhol and Cher, looked on amazed. Penn went on to pin a gatecrashing photographer to the ground.
After two months, they had their first big row over Madonna's desire to attend a peace rally. Sean told her she could not go - and she stormed out.
They made up, but Madonna's former manager, Camille Barbone, declared that she already had the measure of the situation. 'It's stormy and violent. I don't think it will last.'
Worse was to come when the pair flew to Hong Kong in January 1986 to make the movie Shanghai Surprise. The film was a disaster - the first of Madonna's many cinematic turkeys - and by the time it had been made the marriage was hanging by a thread.
Madonna was playing a missionary, Gloria Tatlock, and Penn a conman who was her love interest. Filming was in Hong Kong and Macao. It was one of the few outright disasters of Penn's career.
The pair fought openly throughout over how the movie should be made - both with each other and the director. Penn would tell Madonna that she knew nothing about films and should stick to singing.
Madonna hated the process of filming, fell ill and refused to do a modest stunt which involved falling into water. Penn, a method actor who had learned Mandarin to prepare himself for the role, was not impressed.
There was one violent argument, which ended with Madonna fleeing their
hotel room and Penn banging on the door, shouting abuse.
Triangle: Madonna's former husband Guy Ritchie has become friends with Penn
'You are a paranoid control freak!' Madonna yelled.
'At least I can act!' he fired back. In truth, both were utterly obnoxious on the set. The publicist quit after two days, saying: 'Penn is an arrogant little creep, and his wife goes along with him.'
Former Beatle George Harrison, whose company was producing the movie, reportedly had to fly out to Hong Kong to tell them to grow up and start behaving.
Though Penn would have many tantrums over the media attention they attracted, the real meat of his rages seemed to centre on who was in control in the relationship.
When Madonna was with Penn, she always had her guard up. She told back-up singer Erica Bell: 'It's just too exhausting with Sean. I'm only a woman. How much can I take?'
Penn's drinking exacerbated the problem. In an interview given a decade later, he admitted about his marriage: 'I was not of sober mind during most of it.'
Camille Barbone observed: 'Sean drinks from morning till night.'
In June 1987, Madonna went to the Cedars Sinai hospital for an X-ray after Penn apparently hit her across the head with a baseball bat. At the time, they had been having a heart-to-heart talk about reconciling.
Madonna did not make an official complaint because Penn was about to serve a short jail term for attacking a film extra. He served 33 days of a 60-day sentence in the Los Angeles County jail (23 hours a day in solitary) for violating the probation he'd been given for punching a fan.
He was released into his wife's arms, only for her to throw him out of a taxi a few hours later after yet another set-to.
Their violent arguments were exhausting for everyone, but Madonna hesitated to admit that the marriage had failed. Though she saw lawyers about getting a divorce, she hung on for a full year to see if it could be saved.
It was a decision she would come to regret. In the late afternoon of December 28, 1989, Penn scaled the wall surrounding the Malibu house and found Madonna alone in the master bedroom.
According to a report filed by Madonna with the Malibu sheriff's office, the two began to quarrel. Penn told her he owned her 'lock, stock and barrel'.
When she told him she was leaving the house, he tried to bind her hands with an electric lamp and cord. Screaming and afraid, Madonna fled from the bedroom. What followed was a nine-hour ordeal which left her deeply shaken.
Penn chased her into the living room, caught her and bound her to a chair with heavy twine. Then he threatened to cut off her hair.
According to the police report, Penn was 'drinking liquor straight from the bottle' and the abuse went on for several hours, during which time he smacked and roughed up his victim.
He went out to buy more alcohol, leaving Madonna bound and gagged. Some hours later, he returned and continued his attacks.
Madonna said that he untied her after she agreed to perform a degrading sex act on him. She then fled the house and ran to her car.
Penn ran after her and was banging on the windows of her Thunderbird while she spoke to police on her mobile phone. Fifteen minutes later, she staggered into the sheriff's office.
Lieut Bill McSweeny said: 'I hardly recognised her as Madonna. She was weeping, her lip was bleeding and she had obviously been struck.'
Penn was taken away in handcuffs and charged with inflicting 'corporal injury and traumatic conditions' on her, as well as committing 'battery'.
A week later, Madonna called her lawyers and told them to file divorce papers. Yet she also told Deputy District Attorney Lauren Weiss she wished to withdraw the assault charges against her husband.
The problem was not the publicity - the scandal was in all the papers. It seems she just couldn't bear to see Penn thrown into jail. She still believed that he was the love of her life, and she tortured herself wondering to what extent she was to blame for the abuse.
That perhaps explains why her brother Chris maintains that she has stayed half in love with Penn ever since. That could surely only be possible if she didn't hold him totally responsible for his actions.
At the time, she simply said: 'May God bless and keep him - but far, far from me. This marriage is over.'
But they never truly fell out of contact. When she was with Beatty, Penn called her repeatedly to say that he was too old for her. He called Beatty often, too, to tell him to leave her alone.
They were in touch again as she attempted to revive her film career with Evita, when she declared Penn to be, once again, her friend.
In fact, she welcomed him so warmly back into her life that it's said she invited him to be present at the birth of her daughter Lourdes, in 1996.
And it seems Penn can't quite let her go either. Late last year, while filming Milk, he had to kiss actor James Franco. After the scene, he texted his former wife: 'I just popped my cherry kissing a guy. I thought of you. I don't know why.'
Why would Penn send her this flirtatious - or taunting - message? Perhaps it was a dig at Madonna's close friendship with the lesbian comedienne Sandra Bernhard, which helped end their marriage?
Even today, the emotional bond between Madonna and Penn, which locked them in an unhappy spiral of combat, continues to draw them to each other.
They detest each other, compete with each other and flirt with each other, too.
The scene last weekend was given added piquancy by the fact that Madonna is once again divorced and picking over who or what was to blame.
This makes it all the more fascinating that Guy Ritchie, who has a great understanding of what makes her tick, has chosen this moment to strike up a warm friendship with Penn.
It's enough to make you wonder if the battle of the Poison Penns is about to erupt all over again.