Prince William and Kate Middleton are at the centre of a wave of speculation about the reasons behind the decision to end their four-year relationship.
There had been rumours of an engagement
Possible causes, according to the Sunday papers, include the prince's Army career, his party lifestyle and interference from the Royal Family.
The BBC's Nicholas Witchell believes the prince would have faced pressure to decide if he wanted to get married.
Clarence House has not yet commented on the split.
The break-up is examined in great detail in the Sunday newspapers, although there is little agreement on the reasons for the split of the couple who met at St Andrews University, Fife, in 2001.
Miss Middleton's career and the views of her family have also been cited as causes.
It has been suggested that the prince's move to an army camp in Dorset, and Miss Middleton continuing her life in London, may have put a strain on the relationship.
While Liberal Democrat president Simon Hughes blamed the intense media pressure on Miss Middleton as a factor in the split.
Prime Minister Tony Blair said he thought both of them should be "allowed to get on with their lives".
He told BBC1's Politics Show: "They should be left alone now without reams of stuff being written that I can assure you, from my experience of royal stories - most of which will be complete nonsense."
Our correspondent said his family may well have told the 24-year-old prince to "make his intentions clear" over the relationship.
He said after an awful lot of soul-searching, the couple had decided to go their separate ways in a split that is being described as amicable.
Glare of publicity
Peter Hunt, another BBC royal correspondent, added that the prince may well have sought advice from the queen.
He said: "Prince William is a very cautious individual...he wants to remain in control.
"But I can well imagine that if he had come, in his mind, to a decision that maybe it wasn't working out with Kate, he will have discussed it with his grandparents.
"Prince Phillip and the Queen may well have said to him you need to act because their concern is Kate Middleton left hanging out to dry if there was no prospect, ultimately, of marriage."
Dickie Arbiter, a former royal press secretary, said Miss Middleton could have "troubled times ahead".
"It is going to be difficult for her, difficult in forming a new relationship without the glare of the cameras on her," he said.
"And the cameras are going to be on her for a while to see what she does and how she copes with it."
Publicist Max Clifford said newspaper editors had already made it clear they would pay handsomely if Miss Middleton, or one of her close friends, was to sell their story.
Mr Arbiter said William, meanwhile, would be looked after in the "security and the comfort of the bosom of the Army".
The prince is an officer in the Household Cavalry's Blues and Royals.
Miss Middleton, who works as an accessories buyer for a fashion company, attended the prince's graduation from Sandhurst Military Academy in December.
It was the first time she had attended such a high-profile event, at which the Queen and other senior royals were present.