While Camilla Parker Bowles acted as weekend hostess at Highgrove, telling guests how well her roses were doing in the garden, Princess Diana was often on her own at Kensington Palace, where she would spend hours on the phone to her girlfriends. Once, in 1991, as the marriage dragged on, she apologized to a friend for the background noise, explaining that she was trying to get her tiara on.

With the boys away at school, she set out to make her life less vacant. She embarked on a clandestine relationship with James Hewitt, a cavalry officer, who helped William and Harry with their polo technique (and who in 1994 published a kiss-and-tell about their affair, Princess in Love). In her Panorama TV interview, she said she had been in love with him “but badly let down”. And there was James Gilbey, a Lotus car dealer whom she met when she was 17. Now, she bonded with him afresh over their disastrous love lives. It was Gilbey who called her Squidgy or Squidge 14 times in what became known as the “Squidgygate tapes”. Although they didn’t become public until August 1992, they were secretly recorded by radio hams on New Year’s Eve 1989, when Diana was at Sandringham and Gilbey was in Oxfordshire.

“Oh, Squidgy,” he cried at one point. “I love you, love you, love you.”

Diana was more circumspect in return, but related how she’d just sat through a gruesome family lunch. The Queen Mother had given her “weird” looks and she had felt, she told him, terribly low.

“I nearly started blubbing. I felt really sad and empty and I thought, ‘Bloody hell, after all I’ve done for this f***ing family.’ ”

“I believe that I have a role to fulfill and I’ve got two children to bring up”: Diana with Princes William and Harry in 1995.

The transcript was published by The Sun, whose readers could pay to listen to it on a telephone hotline — and 60,000 of them duly did. Accused of electronic voyeurism, the tabloid offered its profit on the calls to the charity NSPCC, which turned it down.

To the consternation of Patrick Jephson, her private secretary from 1988 to 1996, Diana started consulting a “bewildering cocktail” of clairvoyants, astrologers and soothsayers including one, Madame Vasso, who conducted consultations sitting under a blue plastic pyramid. Jephson worried, he said later, that they “fed the paranoia that never lurked far beneath the surface”.

“I nearly started blubbing. I felt really sad and empty and I thought, ‘Bloody hell, after all I’ve done for this f***ing family.’ ”

Three months before the Squidgygate tapes came out, Andrew Morton had published his book Diana: Her True Story. It apparently drew on conversations with her friends, but Diana refused the Palace’s request that she denounce it in public. The book later turned out to draw on conversations with Diana herself, laying bare her side of the story, including the suicide attempts, self-harm and eating disorder. Aware of her struggle with bulimia, Charles would watch his wife at mealtimes and ask: “Is that going to reappear later? What a waste.”

Diana portrayed Charles as a distant father who put duty first, even when an eight-year-old Prince William was hospitalized for surgery after a school friend hit him on the head with a golf club. Morton recounted how Charles once sent a servant to William’s prep school with plums from Highgrove, whereas Diana would be standing on the touchline when he played football. Privately, there was finally talk of a formal separation. In public, the show must go on.

A month before they separated, in 1992, Charles and Diana couldn’t fake it during a visit to Seoul.

In November 1992 the couple were dispatched on a long-planned four-day trip to South Korea. Diana hadn’t wanted to go at all, and both looked miserable. The Palace pleaded that on one occasion the couple had been at a memorial service, so smiles would hardly have been appropriate, but it didn’t wash. The next month, the prime minister, John Major, announced to the House of Commons that the Prince and Princess of Wales were separating.

“There is no reason,” he added, “why the Princess of Wales should not be crowned Queen in due course.”

The couple, the Palace added, had no plans to divorce.

Anthony Holden, Charles’s biographer, wrote the next year that the prince “was apparently the only man on earth not in love with his wife”.

In the United States, The Washington Post noted that “Diana, with her flash and style, is by far the most popular member of the royal family. Her public appearances always draw large, enthusiastic crowds. The dour Charles attracts few.”

Over the coming years, the beautiful and now separated young princess embarked on the dating she had missed out on as a teenager. She was linked to Oliver Hoare, a married art dealer, and the newly married England Rugby hero Will Carling, who was divorced soon after. In 1995 she embarked on a two-year relationship with Hasnat Khan, a heart surgeon. She enjoyed pottering round his Chelsea flat folding the laundry, friends said, and doing the dishes. She was photographed observing one of his operations, huge, heavily kohl’d eyes peering out above a surgical mask.

The beautiful and now separated young princess embarked on the dating she had missed out on as a teenager.

For the Queen, 1992 was her annus horribilis and one which The Times wondered if the royal family could survive. There was a fire at Windsor Castle. Topless photographs of Sarah, Duchess of York surfaced, having her toes sucked by her “financial adviser”, in front of her two young daughters. When the pictures were published, the duchess was at Balmoral with the rest of the royal family, estranged from Prince Andrew but pending settlement of her divorce. She left the next day in disgrace.

The Squidgygate tapes appeared, and there was a damaging row over whether the Queen should start to pay income tax. Princess Anne remarried, at a time when the Church of England, of which her mother was the head, still disapproved of second marriages, so the wedding took place in Scotland. Now, to cap it all, Charles and Diana’s marriage had gone from being a personal tragedy to a constitutional crisis. Not for nothing did Charles note in his youth, when he was struggling to find a suitable bride, “The last thing I could possibly entertain is getting divorced.”

Two years into a marriage that she described to a journalist as hell “from day one,” Diana flies the flag (and tiara) in South Korea.

The war of the Waleses had begun. Diana, who for years had to run her speeches past Charles for approval, now made pointed remarks in one keynote speech about the importance of showering children with love and hugs. In December 1993 she announced that she was stepping down from public life. It didn’t last. An article that year in Vanity Fair by Holden had described Diana as “the new Britannia, who very much rules the waves … her estranged husband is in danger of being totally eclipsed.”

“Charles,” Holden wrote, “is fed up with having his wife steal his spotlight; he is also weary of having their bad marital vibes drown out his worthy speeches. A future queen more popular and respected than the future king poses an open-ended nightmare for the British monarchy.”

If 1992 was the Queen’s annus horribilis, for Charles it was 1993. In January transcripts of an intimate phone conversation in 1989, between him and Camilla, were published. In what became known as Camillagate, the heir to the throne told his long-term lover that he’d like to live inside her trousers, possibly as a tampon. He was lampooned by cartoonists and some questioned his suitability to rule. Diana’s police protection officer at the time, Ken Wharfe, related how she clutched a copy of the newspaper gleefully and said: “Game, set and match.”

The next year, 1994, Charles gave a TV interview in which he admitted committing adultery, adding that he had remained faithful “until it became clear that the marriage had irretrievably broken down”. On the night of transmission, Diana sashayed into an engagement at the Serpentine Gallery in London, wearing a stunning black cocktail dress and heels and looking radiantly happy. Her butler, Paul Burrell, later said she nearly didn’t go because she couldn’t face it.

In 1994, Prince Charles said on TV that he’d committed adultery. That same day, Diana forced herself to attend an art opening.

The tit-for-tat of the separated couple continued. Jonathan Dimbleby’s biography of the prince, written with his cooperation, said that Charles had resumed his affair with Camilla in 1986, and portrayed Diana as unreasonable, difficult and neurotic, scouring the newspapers for photographs of herself “as if hoping to discover her identity there”. Charles, the book went on, was in “agony” over the situation. “How could I have got it all so wrong?” he wrote despairingly of his marriage, in a letter in 1986.

Diana’s side of the story came in 1995. In an interview with Martin Bashir for the BBC’s Panorama, she admitted adultery with Hewitt. Speaking of her husband’s friendship with Camilla, she said: “There were three of us in this marriage, so it was a bit crowded.” She spoke of how a “friend” of her husband thought she was “unstable and sick and should be put in a home of some sort to get better, so I wouldn’t be an embarrassment”. She would not, she said, go quietly. “I believe that I have a role to fulfill and I’ve got two children to bring up.” She talked about how she had hoped, when she got married, that she would have the support of her husband in facing a daunting future as Princess of Wales. The unspoken message was that she did not. She was open about her struggles with postnatal depression at a time when depression of any sort was never discussed. “It gave everybody a wonderful new label,” she said. “Diana is mentally unbalanced.” Her bulimia and self-harming came about, she said, because “I was ashamed that I couldn’t cope”.

“I’d like to be a queen of people’s hearts,” she told Bashir, “but I don’t see myself being Queen of this country.”

“There were three of us in this marriage, so it was a bit crowded.”

After years of stalemate, the Queen wrote to her son and daughter-in-law to urge an early divorce. It was finalized on August 28, 1996, and Diana was stripped of her HRH title. She told her close friend Rosa Monckton that she thought that was petty, but, Monckton concluded, she didn’t really mind “because she wasn’t somebody who stood on ceremony at all”. By the time of the divorce, Charles had been back with Camilla for more than a decade, and Diana was in a relationship with Khan. She spent the day attending a lunch at one of her patronages, English National Ballet. She wore an immaculate pale blue skirt suit and her engagement ring.

By 1997, Diana was far more popular and beloved than the “dour” Charles.

When Tony Blair became prime minister in May 1997, she held secret meetings with him about her desire to become some sort of roving humanitarian ambassador.

“She had a tremendous ability,” Blair said after her death, “as we saw over the land mine issue, to enter an area that could have been one of controversy, and suddenly just clarify for people what was the right thing to do. I felt there were all sorts of ways that could have been harnessed and used for the good of people.”

Another friend told Morton: “Her head tells her that she would like to be ambassador to the world, but her heart tells her that she would like to be wooed by an adoring billionaire.”

In July 1997 Charles threw Camilla a 50th birthday party at Highgrove, and Diana started dating Dodi Fayed, the son of Harrods’ owner Mohamed Al Fayed. She invited Jason Fraser, a freelance photographer, to photograph her holidaying on a yacht with him in the Mediterranean. In The Crown, Emma Corrin as a newly engaged Diana hints at the complex relationship the princess went on to have with the press, her expression registering both apprehension and excitement. The month before the holiday with Dodi, at Prince William’s suggestion, Diana auctioned 79 of the dresses she wore during her marriage, at Christie’s in New York.

“Diana cleans out her closet,” wrote The New York Times, “and charities clean up.” The dress she wore to dance with John Travolta fetched nearly a quarter of a million dollars. One buyer, who owned a furniture store in Houston, told the newspaper: “We came to Never Never Land to get a piece of the fairy tale.”

“I’d like to be a queen of people’s hearts”: Kensington Palace after Diana’s death, on August 31, 1997.

A Vanity Fair article that month charted Diana’s progress. She had gone from ingenue to glamorous princess, from miserable wife to confident divorcée, from mousy teenager to shoots with Mario Testino, and from Kensington Palace to land mines in Angola.

“She’s living her life as she wants to live it,” Monckton told the magazine, “and she’s free of the restrictions that she had before. She’s much happier with herself.”

The fashion designer Gianni Versace spoke of a recent clothes fitting, at which he said her mood was “serene”, adding: “It is a moment in her life, I think, when she’s found herself.”

The article was headlined “Diana reborn”. A month later, she was dead. Little more than 15 years separate the engagement of Lady Diana Spencer from the funeral of Diana, Princess of Wales. More than 20 years after her death, she remains one of the most famous women in the world.

Season Four of The Crown is out now on Netflix

Hilary Rose is a longtime columnist for The Times, and the author of the weekly column “How to Get Dressed”