Where did the fairytale go wrong?

SHE has a penchant for no-strings, kinky sex; for wearing vials of blood around her neck and being "quite free" with her sexuality. The striking actress Angelina Jolie is also a perfect earth mother to her Cambodian adopted son Maddox and is a Goodwill Ambassador for the United Nations. Oh, and she has a habit of falling for her co-stars.

If any actress is going to send a shiver down the spine of a co-star's other half it is Jolie - and no-one knows this better than Jennifer Aniston.

Superstars Brad Pitt, 41, and Aniston, 35, have been the golden celebrity couple since their lavish wedding in July 2000. But the fairytale came to an end at the weekend when the pair announced they would be separating.

Like most celebrity relationships, their marriage has been plagued by rumours and tabloid scrutiny. Speculation has focused on Brad's keenness to start a family versus Jennifer's willingness to build on her film career after a decade spent playing Rachel in the hit comedy Friends. She reportedly told one friend: "I don't want to be remembered for being an airhead. I want to make serious movies. No-one remembers Robin Williams for Mork and Mindy." Apparently, she also does not see the hurry to have a family, particularly as fellow "Friend" Courteney Cox Arquette had her first baby aged 39.

The decision over whether to have children and when to have them is a dilemma most normal couples face, without living under the microscopic lenses of the tabloids. But there can be few professions which require you to romp with a glamorous co-star coupled with working apart from your spouse for weeks at a time. It begs the question, can celebrity relationships ever work?

To begin with, actors are notoriously insecure creatures who are often surrounded by personal assistants, publicists and adoring fans who are only too happy to fulfil their every wish.

Says Dr Linda Papadopoulos, reader in psychology at London Metropolitan University: "They need to be more esteemed and appreciated and have the adoration from the public, which can be quite inhibiting. Plus they have a lot of people around them who are paid to say "yes" and not "no" and if you're not getting a real view of what is going on, then it can lead to real problems."

But some may argue that the marriage of two actors should bring with it an understanding of the pressures that they face. If you're an actor married to a builder, he may find it hard to believe you had a tough day drinking champagne on set and kissing a man who regularly tops the polls for being the world's sexiest male. Who better to understand the punishing filming schedules and the rounds of mind-numbing publicity interviews across the world than a fellow actor - not to mention the stalkers, the glossy public facades to be kept up and the steamy love scenes with co-stars?

But then not all co-stars come in the form of Angelina Jolie. The moment Brad announced he would be filming opposite Angelina in their forthcoming movie Mr and Mrs Smith, the warning bells would have been enough to wake the dead. This is a woman who married actor Jonny Lee Miller after falling for him on the set of Hackers; who made Kylie's eyes blaze green when she filmed Taking Lives with her boyfriend, the hunky French actor Olivier Martinez; and who was said to have met her match in notorious womaniser Colin Farrell on the set of Alexander.

When she married American actor Billy Bob Thornton their wedding gifts included swopping vials of blood, which they wore around each other's necks.

If Angelina's luminous beauty was not enough to seduce her co-star, there's the image of her as a devoted mother to son Maddox.

While some reports at the weekend blamed the split on Jennifer's reluctance to start a family, others spoke of steamy phone sex sessions between Brad and Angelina, which Jennifer discovered when she picked up the extension at the couple's Hollywood home. Either way, the pressure was building on the couple.

Says Dr Papadopoulos: "When they become couples, they are without each other for extended periods of time and have their every move photographed and commented on. If you or I went for a drink no-one would know or care about it but if they do the same, every aspect of it is scrutinised."

Whether it's tabloid tales of romps with co-stars or cracks in a marriage which is under so much public scrutiny they become gaping chasms, it is hard to see how any relationship can survive in the spotlight - or out of it. Kate Winslet and ex-husband Jim Threapleton shied away from glamorous parties and refused to sell pictures of their wedding to the glossy magazines. They seemed the epitome of normality, enjoying a somewhat quiet life with daughter Mia.

But the pressures they faced as a couple were multiplied when Kate's star rose faster than her North Yorkshire assistant film director husband's, until she eclipsed him. They split up and Kate is now with top director Sam Mendes, with whom she has a baby son, Joe.

Says Dr Papadopoulos: "You tend to get conflicting egos with actors - especially when they're doing the same thing. The one who is struggling may feel guilty and feel resentment while the one who is doing well may also feel guilty and that they can't enjoy or speak about their success or that they're not doing enough for the other person. All this is going to bring a lot of difficulties in how people start to communicate.

"But they are not always doomed to fail. They're a cross section of society where more than one in two couples divorce. The only thing is they're much more prominent."

Those star relationships which have worked include Sean Connery, who has been married to wife Micheline for 30 years. But then the couple are not as juicy tabloid fodder as their younger counterparts.

The James Bond star said in a recent interview: "Micheline and I have pasts - and cultures - which couldn't be more different. But beneath it all we are alike."

It was Jennifer's Friends co-star Courteney who persuaded the couple to join her and husband David in the Caribbean to give their marriage one last go. The pair were even pictured kissing and cosying up to one another as if they were on honeymoon.

But apparently, the trip only sealed their determination to split, another celebrity marriage buried along with the likes of Nicole Kidman and Tom Cruise, Jude Law and Sadie Frost, and Brian and Kerry McFadden.

"This decision is the result of much thoughtful consideration," said the Pitts in a joint statement. "We happily remain committed and caring friends."

Meanwhile the spouse of Angelina Jolie's next co-star may well be quivering in her boots.