Princess Charlotte, the daughter Diana longed for

The Prince and Princess of Wales, Prince Charles and Princess Diana leave St. Mary's Hospital with their new baby son. Photo / AP

For some of those watching, the symbolism must have evoked nostalgic tears; for others sheer pleasure that, one generation on, it had happened at last.

As the Duchess of Cambridge showed her new daughter to the world, with her right arm curled securely underneath, there was Princess Diana's engagement ring, winking happily on Kate's left hand.

Kate Duchess of Cambridge and Prince William smile as they carry their newborn baby princess from The Lindo Wing. Photo / Getty

How Diana would have loved to have been in this position herself, giving Charles the daughter he desperately wanted. Alas, it was not to be.

When, early in the pregnancy with their second child, she had an amniocentesis test, which checks for abnormalities in the foetus, she discovered the sex of the baby. She decided not to tell Charles - instead, she kept secret from him the fact that she was carrying another boy.

Only another mother can realise just what must have been going through her mind throughout her pregnancy - knowing that, ultimately, she was going to disappoint her husband.

"Oh, it's a boy," was Charles's curt observation, when Harry emerged after nine hours of labour in the Lindo Wing at St Mary's Hospital, Paddington, in September 1984. "And he's even got rusty hair."

This was the hair colour of most of the Spencers, including Diana's sister, Sarah.

Princess Diana. Photo / AP

After which, unlike his much more involved son William, who drove his wife and daughter home to their apartment in Kensington Palace, the Prince of Wales went off to play polo.
At that moment, as Diana told friends: "Something inside me died."

What never died was her own yearning, after two boisterous sons, to have a daughter. She even clung to the notion that if she were able to give Charles a daughter it might yet save their marriage.

The Prince had two reasons for wanting a girl. One was that it would enable him to honour his grandmother, the Queen Mother, to whom he was very close, with her name Elizabeth. The second was that two-year-old William was at that time a bit of a handful and he felt having a baby girl around would have a 'civilising influence' on the Kensington Palace nursery.

Princess Charlotte Elizabeth Diana. Photo / Getty

Meanwhile, he has always felt he benefited from having a younger sister, Anne, and considered it to be typically clever of her to have a boy, Peter, and then Zara.

This, presumably, is why he made no secret, when Kate became pregnant with a second child, of the fact that he was hoping for a granddaughter.

In many ways, of course, Kate is the daughter that Diana longed for: sensible, a girl who clearly wants to be seen as a homemaker, and yet, like Diana, has a stylish way with clothes that millions go out of their way to copy. (Not that Diana shopped much for clothes on the High Street as Kate does.)

But she would have adored getting involved with the new baby girl as an indulgent grandmother.

Just how warmly Carole Middleton - who, at 60, would be six years Diana's senior - might have shared the role with William's more glamorous mother is another matter.

But there was another, highly unusual reason behind Diana's unfulfilled desire for a daughter that emerged years later, when the royal marriage was over. It was specifically linked to her love for heart surgeon Hasnat Khan, with whom she enjoyed a two-year relationship and, at one stage, wanted to marry.

She daydreamed that, because of the global fame that had been thrust upon her, having a "brown baby daughter" - as she put it - with Khan, a Pakistani Muslim, could have far-reaching implications for a better and more peaceful world. She believed it would help dispel differences and unite the Muslim and Christian worlds.

In her dreams of having a baby daughter with him, she had even decided on a name: Allegra.

There was no family history in this choice. Allegra was simply the name of the daughter of Lady Sophia Pilkington, a cousin of the Princess's close confidante, Lady Annabel Goldsmith.

Allegra was just five then. Diana liked the name because, from the Latin, it means cheerful, lively and full of energy.

At the time she had paid several visits to Pakistan and visited Khan's family in Lahore. His grandmother, on a visit to London, had been to tea at Kensington Palace.

For Diana, bringing the two very different cultures closer together would disprove Khan's view - the one that she ultimately, and with great reluctance, finally had to accept - that marriage between them would be a mistake and could never work.

But, the fact is, Diana very much wanted a daughter - in addition to William and Harry - for its own sake. She was, after all, one of three lively daughters herself - the youngest girl in the broken family of the 8th Earl Spencer. These were the sisters who nicknamed her "Duch" - short for Duchess - and in whom she confided her doubts on the eve of her 1981 marriage to Charles, and who told her it was "too late - your face is already on the tea-towels".

The prospect of having at least one daughter in a family was one issue on which she and Charles actually agreed - they both believed it would enhance family life.

Prince William, Duke of Cambridge arrives with Prince George of Cambridge at the Lindo Wing following the birth Princess Charlotte. Photo / Getty

In her own case, as she turned from a gauche teenager engaged to the Prince of Wales at 19 into a putative future Queen whose every item of clothing, from top to bottom, was scrutinised, analysed, priced and copied, she yearned to be able to share ideas with a little girl of her own, just as, over the years, Kate will be able to do.

"She longed to have a daughter that she could take out on expeditions to Peter Jones and Harvey Nichols, especially buying clothes for her," recalls one of her friends.

"The boys were great - but mother and daughter out shopping together have a different kind of bond. She missed having that."

She had always enjoyed going shopping with her mother, Frances Shand Kydd. It was especially meaningful after her parents' marriage broke up with an acrimonious court action over custody of the children which Earl Spencer won.

She and Frances were still meeting up for those trips in the early years of her marriage to Charles.

More than anyone, William will be feeling his mother's absence now that he has a daughter of his own.

At the same time, whenever he catches sight of his mother's sapphire and diamond ring on Kate's left hand, he'll know that he and Kate have done just what she would have wanted.