Sir Paul McCartney and his wife Heather Mills McCartney have confirmed they are to separate.
McCartney said in a message on his website that there was "not an ounce of truth" in suggestions that his wife had married him "for the money".
He said: "By now you will have probably heard the unfortunate news that Heather and I are going our separate ways.
"We have issued a statement expressing our sadness at this turn of events but I would like to let people know my feelings about some of the stories which have appeared in the media over the past few days.
"I'm really disappointed that during a very difficult and emotional time for both Heather and myself there are certain people in the media who are writing things about Heather that are just plain untrue.
"It's been suggested that she married me for the money and there is not an ounce of truth in this.
"She is a very generous person who spends most of her time trying to help others in greater need than herself.
"All the work she does is unpaid so these stories are ridiculous and completely unfounded.
"I'm very sad to see that some insensitive people would choose a moment like this to spread these vicious rumours."
In a joint statement earlier today the couple said: "Having tried exceptionally hard to make our relationship work given the daily pressures surrounding us, it is with sadness that we have decided to go our separate ways.
"Our parting is amicable and both of us still care about each other very much but have found it increasingly difficult to maintain a normal relationship with constant intrusion into our private lives, and we have actively tried to protect the privacy of our child.
"Separation for any couple is difficult enough, but to have to go through this so publicly, especially with a small daughter, is immensely stressful.
"We hope, for the sake of our baby daughter, that we will be given some space and time to get through this difficult period."
McCartney's spokesman would not be drawn on the prospects of the marriage ending in divorce, insisting that the couple had merely agreed on a separation.
But a lawyer said that if the break-up went through the courts, it could end up being the biggest divorce case in British history.
It has been suggested that Lady McCartney could walk away with around £200 million of his £800 million fortune despite the couple being married for just four years.
McCartney is Britain's richest musician and made £48.5 million last year from record sales and his US tour.
Leading divorce lawyer Alan Kaufman, head of family law at London firm Finers Stephens Innocent, said: "This will be one of the biggest, if not the biggest, divorce cases to hit the English courts, if it gets that far.
"If I was acting for Sir Paul and he wanted a fight - and he can certainly afford one - I would take it all the way through the courts and argue that a fair settlement would be a lot less than £200 million."
McCartney, who has spent the last two weeks apart from his wife of four years, made his shocking decision known to friends and family today.
Sir Paul was reported to have told one friend earlier: "We really can't go on like this. Enough is enough."
The friend added: "This hasn't just come from Paul. They've decided together that this is the best thing to do. It's by mutual agreement."
The couple had agreed to meet in London for "crisis talks" last week. But according to friends, 37-year-old Heather pulled out in order to stay at home with her sister in East Sussex, where she is recovering from a revision amputation on the leg she lost in an accident 13 years ago.
McCartney, who originally told friends he was planning a trip to New York to see lawyers, is thought to have changed his mind in the hope that he and his wife can sort out their differences.
A 'source' said earlier today: "Paul hasn't come to this decision lightly but felt things couldn't carry on as they were. He and Heather were getting on so badly it became impossible for them to sleep under the same roof.
"It's terribly sad for both of them. We're very concerned itís all over. But nobody has lost hope."
Lady McCartney has revealed in the past that she offered to sign a prenuptial agreement before marrying Sir Paul, but said he turned her down.
The former model said she was prepared to draw up an agreement which would protect the ex-Beatle's estimated £800 million fortune if they split to show that her affections were genuine.
"I wanted to prove that I love him for him," she told Vanity Fair in 2002.
But she told the magazine that she would always remain financially independent.
"I believe every woman should have a reserve, because you never know what will happen in life.
Guys can get bored, especially if they feel they've just got you there," she said.
She gave birth to the couple's child Beatrice, who is now two, in the autumn of 2003.
McCartney already has three children from his marriage to Linda, who died in 1998 - musician James, photographer Mary, and fashion designer Stella.
He also has a stepdaughter, Heather, from Linda's first marriage.