It was, according to one account, a rather wet and windy summer's day when the Prince of Wales first met Camilla Shand at a polo match in the shadow of Windsor Castle.

Maybe it was, maybe it was not: a certain vagueness with the details would be understandable, given that the encounter took place 34 years ago.

During that time they have conducted a passionate relationship, split up, married other people, had a long-running clandestine affair, divorced their respective partners, endured the shame and ignominy of public scandal and the humiliation of the Camillagate tape and, in recent years, led a strange and ill-defined existence in which Mrs Parker Bowles was part mistress, part official consort.

And now this: after 34 years of a love which has shown remarkable powers of endurance but never received official recognition, they are to marry.

It has been a long time coming. Their encounter at Smith's Lawn in June 1971 was the result of match-making by one of Prince Charles's former girlfriends, Lucia Santa Cruz, who announced that she had found "just the girl" for him. It is unlikely that she can have known how right she was.

The pair hit it off immediately. They had plenty in common, of course: their humour, a love of country pursuits, but more importantly Camilla spirited, jolly, unaffected had an exuberance that the anxious and troubled young prince found remarkably attractive. In theory, Charles should not have been romancing her at all, given that she had for many years been seeing his friend Andrew Parker Bowles, a young officer in the Household Cavalry. But Parker Bowles was a man disinclined to be unduly faithful to his girlfriend, and Camilla was beginning to despair of him as a marriage prospect.

Whoever made the first move, it was clear that Camilla did not need too much encouraging: witness her famous remark to him at a party soon after they met, when she reminded him of the relationship between her ancestor Alice Keppel and King Edward VII: "My great-grandmother and your great-great-grand-father were lovers. So how about it?"

Their relationship seemed destined not to last, however. Charles, then embarking on a naval career, was plagued with indecisiveness, and went off to serve in the Caribbean for eight months without telling her what she meant to him. By the time he returned she and Parker Bowles were engaged.

On the face of it, that should have been that. Camilla seemed ideally suited to the life of an Army wife, and Charles had his work cut out dating a succession of pretty girls and working out which would make a suitable future queen. Yet, somehow, the glowing embers of their affair refused to die down, and before long the fire had been rekindled.

Their friendship continued throughout the early years of marriage to Parker Bowles, and even if it was not physically consummated immediately, by 1980 Camilla was sufficiently established in his life to provoke a major row between Charles and his then girlfriend, Anna Wallace, when the prince spent a party dancing with Camilla.

Then Diana arrived on the scene, and a world hungry for romance lapped up every detail of the burgeoning love between the prince and his beautiful young bride. We, the public, did not find out until much later that the fairytale was more myth than reality. Diana, perhaps, had reason to doubt Charles long before they married.

In November 1980, before their engagement, the Sunday Mirror claimed Diana had spent several hours one night with Charles on board the royal train as it stood in a siding. Denials were issued, and indeed the story was wrong in one crucial detail: the blonde assumed to be Diana was Camilla. Diana, for all her alleged naivety, cannot have failed to have worked out what was going on.

It was no surprise to learn later that Diana considered calling the whole thing off and indeed if she had known, as has since been alleged, that Charles slept with Camilla at Buckingham Palace for what he believed was the last time in the week before the wedding, it is highly unlikely the wedding would have gone ahead at all.

On honeymoon the subject of Camilla came up yet again. At a dinner on the royal yacht Britannia for President Sadat of Egypt Diana noticed Charles's cuff-links. As she recalled on the tapes which formed the basis of Andrew Morton's book, and which were broadcast last year on US television: "So I said: 'Camilla gave you this, didn't she?' He said: 'Yes, so what's wrong? They are a present from her.' And boy, did we have a row'."

For many years the accepted wisdom has been that Diana was the first to break her marriage vows: as Charles told Jonathan Dimbleby, he did commit adultery, but only after the marriage had "irretrievably broken down". Considerable doubt has been placed on this version of events, but the issue has never been satisfactorily resolved.

The Prince's friends maintain that he only went back to Camilla after Diana had had an affair with her personal protection officer, Barry Mannakee. Diana's supporters insist she only sought comfort with Mannakee because she had as good as lost Charles to Camilla.

As she put it so memorably: "There were three in the marriage, so it was a bit crowded."

Certainly by 1986 the Prince was seeing Camilla on a regular basis, and by 1989 their relationship had become so serious that Diana confronted Camilla at a party demanding they end their affair. Diana recalled on the tapes: "She said to me, 'You've got everything you ever wanted. You've got all the men in the world in love with you and you've got two beautiful children, what more do you want?' So I said, 'I want my husband.'"

Up until 1992, Charles's triangular marriage had remained a more or less private matter. Then came Morton's book, which named Camilla as Charles's mistress for the first time, followed by the excruciating Camillagate tapes: once heard, Charles's fantasy of being reincarnated as a Tampax was something never to be forgotten.

The effect was to cast Camilla as the villain in the ongoing break-up of Charles and Diana's marriage. Nicknamed the Rottweiler, even when both sides were divorced, she was vilified at every turn while Diana occupied an ever more saintly position in the public imagination. When Diana died in August 1997 there was a renewed outpouring of resentment against her.

In the immediate aftermath of Diana's death, the prospect of Charles and Camilla ever getting married seemed very distant indeed.

Not only was there no question of the public ever accepting the notion of Queen Camilla, but there was also the fundamental obstacle of whether the prince as the future head of the Church of England would be allowed to remarry.

The royal family did not make things easy, either: for years the Queen avoided Camilla, and other members of the family often pointedly ignored her.

Slowly and far from steadily, the campaign was waged to win acceptance for Camilla. Finally, after the years of tumult, pain, subterfuge and public vilification, their patience and enduring love is to be rewarded. They have come a long way from that damp afternoon at Smith's Lawn.