MAYBE it was partly because the Princess of Wales was so beautiful, so young, so transparently nave when she took part in that fairy-tale wedding, that everyone hoped and believed the marriage would be a success. And so, at first, it was. Not until after the birth of her second child did the belief that her husband was essentially selfish and unfaithful take root in her mind, and only after the age of 26, when she ceased to sleep with him, did it become clear that an effective separation was inevitable.

Poor Princess Alexandra. The fate of that previous Princess of Wales has eerie similarities to that of her successor. Royal history, like any other family history, is a matter of repetitive patterns. The job entails the same gilded cage of strict protocol and constant observation, which makes it hard to bear. The heir to the throne is traditionally under tremendous strain, and the burden of a lonely, fettered upbringing.

The rows between the royal couple must have raised deafening echoes around the palace walls. The young Alexandra was as beautiful as Diana, she dressed with the same elegance, she was just as obstinate, just as kind and diligent in charitable work. Camilla Parker Bowles, of whose influence on Prince Charles Diana was reportedly jealous in the early stages of her marriage (though no evidence has been produced to suggest they were more than friends), is even descended from Alice Keppel, one of the most famous and discreet mistresses of Alexandra's husband, Edward VII. It is all as sad now as it was then.

What is new is not Diana's position as an unhappy royal wife of an unhappy husband, or their decision to separate their lives and appear together only in public and on family occasions.

The problem is not that she was not born royal: how well are those born royals, Princesses Stephanie and Caroline of Monaco, setting an example of old- fashioned family life? No, the alteration lies in the Princess's attitude to her dilemma, and that attitude is, like that of Stephanie and Caroline, a reflection of her age. There has been a fundamental shift in women's expectations since Alexandra meekly accepted her lot as mother and cipher wife. Diana has broken the tradition of public sham closeness and shattered her gilded cage with a startling crash which proclaims that alteration.

She has fought for an independent life as a Career Princess and a public, even parliamentary, acknowledgement that the fairy-tale is fiction. Her action is aimed at showing that she has a public job to do in the Royal Family in her own right rather than as her husband's wife. The blushing girl who used to curl up with a novel by Barbara Cartland has grown up into a woman of whose actions Barbara Cartland disapproves. Diana has, as the Virginia Slims cigarette advertisements used to say, come a long way.

There is no question that this startling development in royal affairs is Diana's doing. It is clear from Andrew Morton's book of her life that she gave implicit approval to its contents, that she wanted everyone to know the fact of her misery.

The strain of being thought to be living in a glorious land of tiaras and titles and happy-ever-afters when she was, in fact, so disturbed and lonely that she was attempting suicide and even, at one point, expressing her grief by 'cutting up' - a practice more familiar within the walls of Holloway than the metaphorical prison of Kensington Palace - was too much to take.

It was not the media who forced the couple to part. Over the years Diana has learnt how easily news media that cannot be controlled can be manipulated. On their famous trip to Korea this year she needed only to take her husband's hand now and then, to smile up into his face, to lean her head on his shoulder, and the tabloids would have been a blaze of royal reconciliation headlines. But neither was prepared to play charades. The headlines that resulted from their stiff public deportment were what was needed to convince the Queen that separation was inevitable. Diana is still the mother of the heir to the throne - there was no question of her leaving the Royal Family with as abrupt a break as the Duchess of York.

It is impossible to blame a woman as desperate and miserable as the Princess of Wales for her actions. It is equally hard to blame Prince Charles, a thoughtful, kind man, but one whose formal upbringing could not have begun to prepare him for the care of a girl so fearful of rejection that her actions sometimes seemed designed to bring rejection about, so insecure and, at times, so hysterical as a result.

Add to that a marriage with a 12-year age gap, Diana's youth on her wedding day and their disparity of interests and no one should be surprised at the result. The surprise is that she has managed, against this background, to develop such self-confidence, the sense of which blazed out behind John Major's public declaration. She is a woman transformed since the self-deprecating days when she banged her head in public and said ruefully that it didn't matter, there was nothing inside. How did such a metamorphosis from finishing-school Sloane come about?

Nothing in Lady Diana Spencer's background suggested that she was going to break the mould of her upbringing. From early childhood she was conscious that girls were second-best: that she probably would not have been born if her parents had not been trying for an heir to her father's title, and of their disappointment at her gender. It might have been untrue, but that was her first feeling of rejection. Her life went on as a typical upper-class girl of her generation, whose brother was sent to Eton, but whose father placed such little emphasis on a daughter's academic record that he allowed her to leave school with no O-levels, with only a county show prize in guinea-pig keeping on which to base her judgement of her intelligence. Her career after school took a predictable turn as a result: she earned money as a cleaner and an unqualified nanny.

Her upbringing, in short, was based on an assumption unchanged since the Queen Mother was a girl: marriage and babies were an aristocratic girl's career. So she married Prince Charles and stayed in the Victorian era: wearing jewellery to show her husband's status, her choice of clothes and furniture her chief channel of self-expression. And then her self-image, remarkably, began to change. What altered it was the unexpected discovery that she was extremely good at doing the royal job, the business of meeting, and chatting and listening; better, in some ways, than some born to the business; better, in some ways, than her husband.

She had an excellent public manner. Prince Charles's shyness can be painfully obvious; hers is hidden. Her own unhappiness made her empathise with the unhappiness of others she met on hospital sick-beds and in the counselling groups of her charities. Unlike the rest of the Royal Family, she had no inhibitions about touching and hugging. She even learnt, to her own surprise, to deliver speeches, take responsibility for their content and put them over with sound bites that sometimes snatched the headlines from her husband. Her charity work began to move into more controversial areas, particularly those of Aids and family breakdown. Lacking private satisfaction, she took her pleasures from what had become a career. And, like many women of her time, she discovered that this career had given her the confidence to act more decisively in her private life.

And so when, whether it was true or not (pressing the last-number redial button on her husband's portable phone seems an unsatisfactory, if technologically up-to-date, way of proving infidelity), she believed that her husband had rejected her love, she did not make the traditional response. Instead, she modernised the monarchy.

Whether her idea of setting up a rival and separate shop in the royal business will work is another matter. Royalty has never before been in the equal opportunities business. The public may well find this cold dose of reality too chilling to enjoy.

Sympathy for a suffering princess is one thing: sympathy for a princess who has decided to go it alone surrounded by pomp and plenty is another. Every dinner that the Prince or Princess go to, every glance that they make to a potential lover, will be monitored by the press. Just to make life more interesting for the Royal Family, the Kitty Kelley biography of the Duke of Edinburgh is on the way. It would be a pleasant but astonishing surprise if it did not reveal that the marriage of the Queen has not always been as blissful as her subjects would like to think.

Can the Princess of Wales, rocked by these events and exposures, prevent herself from falling in love and deciding one day, like many women of her generation, to give marriage a second chance? Recently she is said to have prophesied that she will not hold the title of Princess of Wales for more than 15 years. If she is right the Career Princess has just over three more years to serve.

(Photographs omitted)