Falling apart? Brad Pitt, sporting a goatee beard for a new film role, and Angelina Jolie in New York last month

Early evening last summer at Brad Pitt and Angelina Jolie’s Los Angeles mansion. An army of multicultural nannies has put the couple’s six children to bed and the staff – ever fearful of ferocious rows between the two – are hoping for a calm night.

Pitt is relaxing in his bedroom, smoking cannabis and listening to reggae. In her separate suite, Jolie is reading a classic novel.

Then it begins, as it has so many times. The screaming and swearing. The wild accusations of affairs on both sides – Jolie with a young actress, Pitt with an African model.

It is the latest in a series of rows sometimes so loud and abusive that the staff have felt obliged to remove the children from the house.

That the pair would be in the same house at all is a surprise to those in their inner circle. Many assumed the once-golden couple would split two years ago, but they decided to give their relationship another go.

Time and again, Jolie, 34, has made dire threats over what she would do if 46-year-old Pitt left. Time and again, he has returned even if, as friends suggest, his health is suffering.

If the enforced closeness was supposed to rekindle one of the most talked-about romances on the planet, it has failed. If anything, it has fuelled the couple’s mutual hatred. The relationship was rickety before; now it is a shell, a facade to protect the double A-list Brangelina brand.

‘Brad has called Angie names not worth repeating on many occasions during the past few months,’ a close friend of Pitt said. ‘He’s fed up. I have always said that they’d split sooner or later. It appears it will be sooner.’

The couple planned to take a holiday with their children to the Caribbean early this year. According to a friend, they cancelled plans after a huge falling-out last month. ‘They have barely been together since,’ the friend said.

Pitt, bruised by the rows with Jolie, has been spending time with actress and producer Drew Barrymore, although it is unclear whether their heart-to-hearts amount to romance or just comfort and counselling.

The only thing that has so far stopped Pitt and Jolie from permanently splitting was not the question of how their £200million fortune would be divided, but lawyers’ negotiations over who would get custody of the children.

News of those negotiations surfaced a fortnight ago in a flurry of newspaper stories and internet gossip. Anonymous sources then countered by insisting the discussions were merely to draw up an agreement to be used in the event of the couple breaking up. Last week, there was still silence over the allegation.

Leading lady: Angelina Jolie at the premiere of Brad’s film Inglourious Basterds last year

The lawyers were discussing division of their wealth and custody of their family, so the rebuttal carries an element of truth. But the split is not hypothetical – it will be soon.

I can confirm that a deal has now been done, but do not expect an announcement from their lawyers. Instead, Pitt will follow the strategy used by his close friend Guy Ritchie when he and Madonna split in 2008 – silence for months, then a sudden official announcement of divorce.

That pattern has certainly been played out so far. Jolie’s manager Geyer Kosinski, usually swift to kill rumours, has been strangely reticent.

A close friend of the couple told me that any attempt to dampen down news of the ‘split’ should be taken with a pinch of salt.

‘No one close to them has gone on record to deny anything. The couple are finished,’ said the friend.

Whenever the statement comes, Jolie is already mapping her future. By the time the break-up is formally made public, she will have her eyes on a new man. As in the past, it is likely to be someone already in a marriage or attached. Jolie’s romantic ambitions now run far beyond showbusiness.

Instead, she wants someone more worldly, more serious. Like Carla Bruni, who abandoned dalliances with pop musicians for the French President Nicolas Sarkozy, Jolie sees herself on the arm of someone on the world stage.

No longer the troubled teenage bad girl, Jolie has cleaned up her act, at least for public consumption. The image she paints for herself is saintly but still 𝑠e𝑥y, an haute couture humanitarian.

There are only two role models she now wishes to emulate – Jackie Onassis and Diana, Princess of Wales. A close friend says Jolie believes she can be this era’s Diana. She told me: ‘She thinks she can be a similarly powerful and charismatic figure in global political circles.’

Jolie is a generous benefactor of charities, a human-rights campaigner and a UN goodwill ambassador. She is determined and – certainly by Hollywood standards – ferociously intelligent. Now, she believes, is her time.

I am an undercover investigator and author. By pretending to be a hairdresser, I inveigled myself into Michael Jackson’s inner circle, becoming the first person to predict his death, six months before the tragedy.

Jackson’s people were often talkative, revealing strange stories about him. Jackson never challenged the gossip, concluding that the weirdness merely added to his mystique.

By comparison, the Brangelina image is tightly policed. Mr Kosinski controls everything. The only ‘leaks’ are authorised by him. Breaking into Team Brangelina, I soon found, was going to be a harder nut to crack than Jackson.

I got my big break in the summer of 2008 while mingling with the paparazzi outside Chateau Miraval in Provence, where Jolie was spending the last few days of her pregnancy.

When journalists chased her to the Nice hospital where she gave birth to twins Vivienne Marcheline and Knox Leon, I stayed put. It gave me the opportunity to befriend one of her inner circle at the chateau – the start of a connection that yielded many of the stories that appear in my book Brangelina, published late last year.

In it, I predicted that their relationship would not last, riven as it was by vicious fights. I was told that Jolie was nervous about what the book would say about the couple. But even I was surprised by how she reacted, showing once again that she is a mistress of the dark arts of spin.

Rather than denying everything, Jolie decided to outflank me, declaring to Das Neue, a German magazine, that she didn’t believe fidelity was essential for a relationship.

‘Neither Brad nor I have ever claimed that living together means to be chained together,’ she said. ‘We make sure that we never restrict each other.’

She appeared to be confirming that she had an open relationship with Pitt, something her inner circle had talked about for years. It was the beginning of a campaign to prepare the public for an eventual split.

She also admitted she got so angry with Pitt that she sometimes tore his shirt. The remark was perhaps an echo of the behaviour that first attracted Pitt to Jolie, whom he met when they started filming the thriller Mr & Mrs Smith in 2003.

Pitt was captivated by the wild 𝑠e𝑥 he enjoyed with Jolie. It was, as one friend put it, less of the Kama Sutra and more a carnal version of the Cirque du Soleil. They often stayed in bed for 18 to 20 hours at a time.

A limousine driver told me: ‘I used to drive them both all the time.’ In the beginning of their public relationship, he recalled, they were affectionate. Twice he said he saw them ‘going at it in the back seat’.

By 2007, however, the mood had changed. They once had an altercation in the car, with Jolie the more violent of the two. ‘She really flew off the handle, threatening him and lashing out at him. She has a temper like a cobra.’

A woman who worked with Pitt while he was filming Troy also talked of tempestuous scenes.

‘Apparently it’s always him that ends up moving out,’ she said. ‘But then he ends up coming back, and nobody knows what happened to bring him back.

Humanitarian image: Angelina Jolie visiting New Delhi in 2006 in her role as a UN goodwill ambassador

‘Partly, I think he really does love her. Partly, he considers them a family, and he loves that element of it. He’s supposed to be a great dad with those kids. And partly, there’s the whole Brangelina thing.

‘If you knew Brad, he’s very earnest. But then again, I don’t know how he can handle her crazy temper.’

From the start of her career, Jolie had proven a smooth media operator, wriggling out of potential PR disasters that would have flattened lesser personalities. In 2000, she publicly outed her affair with the actor and writer Billy Bob Thornton – usefully quashing rumours of an incestuous relationship with her brother James Haven, which they have both denied.

The gossip about Jolie’s brother had started when she kissed him passionately at the Oscars ceremony at which she won best supporting actress for Girl, Interrupted. I discovered that she was also seen kissing Haven at other events, including the Golden Globes.

If one taboo remains in Hollywood, it is incest. After the story broke, studio executives threatened to blacklist Jolie, so she suddenly announced her affair with Thornton.

When more problems threatened her two years later, she used misdirection to get out of another scrape, deflecting accusations that she bought her adopted son Maddox from his destitute mother in Cambodia. This time, she declared she and Thornton had split. Changing the subject again won the day.

Jolie certainly needed all the skills she could muster in 2004, when rumours first swirled that she was having an affair with Pitt. He was married to Jennifer Aniston, and his new lover did not want to be seen as a home-wrecker.

Aniston was painted as a woman who did not want to give Pitt children. ‘Insiders claim Pitt’s desire to start a family and his wife’s reluctance to give up her career have caused intolerable pressures,’ wrote one newspaper. By 2005, Pitt and Aniston had announced their break-up.

‘It was Angelina who came up with the whole story about Jennifer not wanting to have kids,’ said a source connected to the publicity department at Fox. ‘She was convinced the story would resonate with women who saw her as a man-stealing bitch.’

There are indications that neither Pitt nor Jolie has been committed to monogamy. Two members of Pitt’s family and someone in Jolie’s inner circle who sees her almost every day have told me that he has for months been accusing her of infidelity.

A 21-year-old actress with connections to the entertainment industry has been saying that she has had a two-year affair with Jolie – a relationship corroborated by emails.

Friends say Jolie has had at least a dozen lovers – male and female – over the past four years. Then there is Jenny Shimizu, the boyish Japanese-American actress with whom Jolie had an affair on the set of Foxfire in the mid-Nineties.

Public togetherness: Brad Pitt and Angelina Jolie with their children Zahara and Shiloh in 2007

Shimizu said in 2007: ‘She’s always had lovers that she relies on.

‘If she can ring you and you can meet, then she can take care of her 𝑠e𝑥ual needs. Whenever she calls me, I visit her.’

Pitt has turned to other women, too – a source of further clashes with Jolie. His name has frequently been linked with the beautiful Sudanese model Amma, whom he met at a Darfur benefit at the 2007 Cannes Film Festival. He was seen with her on at least one other occasion.

After my book’s publication, Jolie and Pitt seemed to be constantly photographed with their children. They were together with their daughter Shiloh, three, and their adopted daughter Zahara, five, on the set of the movie Salt, starring Angelina, in New York. Pitt was also seen with his sons Pax, six, and Maddox, eight, at a New York restaurant.

I expect to see further such photo opportunities over the next few weeks as the couple try to calm the storm while the lawyers iron out the minor details of their separation.

Of course, there is no way Pitt and Jolie could spend so much time with their children without help. Indeed Shiloh was heard to refer to one of her nannies as ‘Mommy’ within earshot of a staff member at The Dorchester hotel in London.

This is not to suggest that Pitt or Jolie are anything other than good parents. The children are the one thing that has stopped Pitt walking out already. He is at heart a simple country boy, certainly not as cunning as Jolie, and is content to revel in family life. He is an honourable man and is determined to be with them.

It was that insistence that held up the settlement of their split. Pitt initially wanted full custody at least of their biological children – Shiloh, Vivienne and Knox. Equally, Jolie wanted to be their sole custodian.

Now it has been agreed that the couple will have joint custody of all the children. Pitt and Jolie will be required to live in close proximity and be jointly involved in decision-aking.

The other thing preventing Pitt leaving her is a genuine concern for the effect it would have on Jolie’s health.

For most of her life, Jolie has suffered from emotional instability. She has said she contemplated suicide several times as a child, and later when she lived in New York she planned to end her life with a knife or pills but couldn’t go through with it.

In 2000, she was admitted to the Resnick Neuropsychiatric Hospital in California. Hospital insiders said at the time: ‘She was very angry and thought she might kill herself if she wasn’t treated.’

A woman who worked on the set of Mr & Mrs Smith claims Jolie is erratic. ‘Everybody who’s seen her knows what I mean,’ she told me. ‘She’s not unpleasant. Just erratic.’

The unpredictable behaviour has continued. In the spring of 2009, Jolie was reported to have collapsed on the set of Salt. Photos emerged showing her looking unnaturally skinny. The explanation given was that she had been on a ‘liquid detox’ diet that had left her weak.

Lost love: Brad Pitt with his ex-wife Jennifer Aniston in 2000

I spoke to a senior member of the Salt crew who saw the incident. ‘I wouldn’t call it a collapse,’ he told me. ‘There was an episode.’

It is Pitt, however, who has suffered the most during his five years with Jolie. He appears to have aged at least 20 years. Friends say there is never a day when he doesn’t stare at his paunch in the mirror. One insider says: ‘Look at a photo of him four years ago and look at him now. He is ragged.’

A decade ago, it would be hard to find a young woman who wouldn’t admit she’d like to sleep with Brad Pitt. Few will say the same of the lumpy figure seen in Manhattan recently.

Then there is the long goatee beard, which he is growing for a new role. At a distance, it gives the impression of an old man who has dribbled food over his chin.

The decline in Pitt’s appearance is mirrored, according to insiders, by deteriorating health and the fact that he smokes cannabis more than ever.

Friends of Pitt remark that at the start of each of Jolie’s big relationships she was the junior partner in terms of celebrity, but by the end emerged as the bigger name. It is almost as if she has taken a transfusion of fame and then abandoned her men.

As members of her family have said: ‘She takes them and she runs them into the ground. That’s her modus operandi.’

The love between Pitt and Jolie may be long gone, but the financial chemistry of two big names entwined is still worth millions. As one of Pitt’s relatives put it: ‘Brangelina is no more. Now there is only Brand-gelina.’

Saddest of all, Pitt has confessed to friends that if he could turn back time, he would have stayed with Jennifer Aniston. That speculation was heightened when Pitt and Aniston separately attended a Haitian fundraising concert in Los Angeles last month.

But there is no hope of his getting back with Aniston, who has declared that she wouldn’t sleep with him again after he’d bedded Jolie, even if he wore six condoms.

Jolie’s thoughts are now moving far beyond the end of her relationship with Pitt and on to the next phase. She is 34, sharp and icily glamorous, the sullen, gothic looks she had in her 20s replaced by a classic elegance more in keeping with a Diana-obsessed social climber.

Jolie has always been drawn to married men or those already in a relationship. Despite attempts to portray herself otherwise, she has been a home-wrecker. This psychological flaw has been put down to her tempestuous relationship with her divorced father, the actor Jon Voight. Some say Jolie feels the need to prove she can possess any man.

It is also clear that she needs someone to care for her, despite her dominating ways. The affairs that have caused such ructions in her household are sideshows. She will be looking for a man to elevate her status beyond bad-girl-turned-good to a 21st Century People’s Princess.

So who might she have set her sights on? Here speculation tilts into the fanciful. Some insiders suggest Bill Clinton, or even, bizarrely, Prince William.

Whoever she chooses, we can be sure that the passing of the super-couple known as Brangelina will not be an end for Angelina Jolie – just a new chapter in the story. Never underestimate her.