It was a fine day in February 1981 when Prince Charles announced his engagement to Lady Diana Spencer. Hundreds of photographers lined up in the garden of Buckingham Palace, taking thousands of pictures for front pages all over the world. The weeks leading up to it had been a scrum. Diana was besieged at her flat in Earl’s Court, west London, and at the kindergarten where she worked. She consoled herself with the thought that, once the wedding was over, she would return to a life of relative obscurity. The royal family, too, believed that the fame of this shy, teenage virgin would be transitory. More to the point, as far as the royal family were concerned, Prince Charles was 32 and in need of an heir. Diana was 19.

“Everyone,” Andrew Morton wrote in his biography of Diana years later, “even newspaper editors, was caught unawares by the Princess Diana phenomenon. Their readers could not get enough of Diana.”

Flashbulbs punctuate rumors that Diana, here heading to work as a kindergarten teacher, is romantically linked with Charles.

To the public, theirs was a fairy-tale romance; the pretty aristocrat, described by her friends as “gentle and shy”, had bagged the most eligible bachelor in the world. They met only 13 times before the engagement, but Diana was besotted. She confided in friends that she thought his wooing slightly odd, because he wasn’t very tactile. Then again, she’d never had a boyfriend. The night before he proposed, he called to say he had something important to ask her. She sat up all night deliberating with the girlfriends who shared her flat, where her bedroom door had a sign on it saying “Chief Chick”. Vanity Fair reported that he proposed next to a cabbage patch in Camilla Parker Bowles’s back garden. Diana said yes.

“I feel positively delighted and frankly amazed that Di is prepared to take me on,” Charles told reporters.

The pretty aristocrat, described by her friends as “gentle and shy”, had bagged the most eligible bachelor in the world.

Diana was the product of an unhappy childhood. She was brought up at Park House on the Sandringham estate, with her siblings, Sarah, Jane and Charles. She was seven when her parents divorced and 14 when her father inherited the title and the family moved to Althorp in Northamptonshire. Her father later remarried a woman, Raine, whom the children disliked. The family mixed in royal social circles, so she knew the unspoken rules and complex etiquette surrounding the royal family — she passed what the new series of The Crown calls the Balmoral test.

“It wasn’t as though I was picked out like My Fair Lady and told to get on with it,” she told Morton. “I did know how to react.”

What she didn’t yet know was how to dress. Once Diana was engaged, Anna Harvey, the fashion director of British Vogue, was recruited to help the future princess with her style. She went on to become a friend.

“She had sparkle,” Harvey said of their first meeting. “It was simply magnetic.”

Going public: the Prince and his future Princess feed the fairy tale.

Only a month after the engagement, a picture caption in The New York Times read: “Lady Diana Spencer, Prince Charles’ fiancée, upstages him at Goldsmith Hall concert with her off-the-shoulder chiffon gown.”

But Diana had no idea how to deal with the pressure and attention that came with her engagement, and no help from the Palace. She later admitted that it took her six years before she felt comfortable with her new role as the star of the show. Just before her wedding, she told her dance teacher: “In 12 days’ time, I shall no longer be me.”

She also discovered that the man she was about to marry had sent a bracelet to his old flame, Camilla, with the intertwined initials of their nicknames, Fred and Gladys. He dismissed it as a gesture of friendship. She sobbed through the dress rehearsal at St Paul’s Cathedral and considered calling the whole thing off.

“Too late,” her sisters told her. “Your face is already on the tea towels.”

Even The New York Times was excited. On the eve of the wedding, it reported that Prince Charles had lit the first of 101 beacons that were now “burning across a joyful Britain”.

“Romantics found an extra sweetness,” the paper continued, “in the obvious fact that Prince Charles, a highly popular figure, is marrying for love, and not for dynastic convenience.”

Diana said later that she felt like a lamb to the slaughter. Outside her bedroom window at Clarence House, home of the Queen Mother, crowds gathered on the Mall, while in Hyde Park there was a firework display. Years later, she admitted that she was already suffering from bulimia. Charles had put his arm round her one day, after they were engaged, and remarked that she was chubby. The night before her wedding she made herself sick.

Dating Prince Charles meant Diana was always on display, even in her apartment.

On July 29, 1981 a million people took to the streets of London to watch Diana and her father make the journey, in a glass coach, to St Paul’s. She had just turned 20 and would become the first royal bride to omit “obey” from her vows. Debrett’s predicted that it would be the last, great state event of the 20th century and it was watched by a TV audience of 750 million people in 74 countries. Her brother, Charles, said that it was the first time he had ever thought of Diana as beautiful. The dress, designed by David and Elizabeth Emanuel, was supposed to be highly romantic and big enough not to be swamped by the vast interior of St Paul’s. Instead, it swamped the bride.

The happy couple honeymooned first at Broadlands in Hampshire, home of the late Earl Mountbatten. Murdered two years before by the IRA, Mountbatten had hoped that Charles, who idolized him, would marry his granddaughter Amanda Knatchbull. The couple then cruised round the Mediterranean on the Royal Yacht Britannia. Charles read Diana books by his hero and mentor, Laurens van der Post, and encouraged her to analyze them over lunch. Dinners were formal black-tie affairs, in the company of the ship’s officers, and the couple stopped off in Egypt for an official visit. Finally, at Balmoral in Scotland, with the rest of the royal family, he took her on bracing walks and read her Jung. One day, when they were conferring over schedules, Charles opened his diary and photographs of Camilla fell out. By the time they returned to London, Diana was making herself sick four times a day. She later confided in Max Hastings, editor of The Daily Telegraph from 1986 to 1995, that the marriage had been hell “from day one”.

By October 1981 she was painfully thin, in the early stages of pregnancy with Prince William and suffering from bad morning sickness. She was also finding the attention unrelenting and overwhelming. She complained later that she was expected simply to adapt to being Princess of Wales overnight. She felt under enormous pressure to be a perfect princess and she missed her old life. Harvey recalled that for a time after her engagement, “she used to go shopping in Sainsbury’s for little things like yoghurts, because she was so desperate for normality. She soon had to give that up because she was mobbed.”

Horsing around: Camilla Parker Bowles and Diana watch Prince Charles compete in an amateur steeplechase in 1980.

For the nation, the Charles and Diana love story was a reason to be cheerful in a year of grim news. More than two and a half million people were unemployed, and there were riots all over the country, including Toxteth in Liverpool and Brixton in south London. For the royal family, Diana was a welcome boost of glamour. Harvey said that all Diana owned when they first met were “a few Laura Ashley skirts and some bobbly jumpers. That was it.” But when she visited Vogue before her wedding, and Harvey met her in the flesh, she recalled, “I took one look and thought, ‘This isn’t going to be too difficult.’ She was about 5ft 10in and completely in proportion. Her eyes lit up when she saw all the racks and her enthusiasm was contagious.”

From then on, Harvey would take rails of clothes to Kensington Palace, all of which were paid for if they met with approval. The two women would sit on the floor of Diana’s drawing room, looking at sketches and swatches and drinking endless cups of coffee brought in by the butler.

The Charles and Diana love story was a reason to be cheerful in a year of grim news. More than two and a half million people were unemployed, and there were riots all over the country.

“At the start she was incredibly unsophisticated, but she was very open to ideas,” Harvey said. “The fashion press would have liked her to be more fashionable, but it would have been completely inappropriate. She wanted to be modern rather than fashionable and she rapidly learned how to make an impact.”

Even at this early stage she was also determined, as far as possible, to do things her way. Harvey ordered dozens of pairs of suede gloves to go with every outfit because, at the time, the royal family always wore gloves. They were never worn. Diana preferred flesh-to-flesh contact, Harvey realized, and less formality. Harvey lamented that the one thing she could never persuade her to ditch was her chunky costume jewellery. With all the jewels in the world at her disposal, the princess thought it was funny to fake it. Over the years, Harvey noted, as Diana became more confident and independent, “the heels got higher, the skirts got shorter. Everything became more streamlined and athletic in line with her role as a committed charity worker.”

The paparazzi’s (eventually tragic) pursuit of Diana was in full swing in London months before the royal engagement.

In 1981 her first visit as Princess of Wales to the principality was greeted with vast crowds, pouring rain and terrible morning sickness. In public, she was radiant and charming. In private, she was often in tears between events, telling Charles that she was unable to face the crowds.

“They’ve come to see my wife,” Charles joked glumly to aides. “They haven’t come out to see me.”

She worried constantly if she was good enough, and her relationship with her husband was already unraveling. When she was pregnant with William, in January 1982, she attempted suicide by throwing herself down the stairs at Sandringham. There would be four more attempts over the years, which were, friends said later, a desperate appeal for help from a young woman who, only six months after her wedding, was lonely and unhappy.

“Charles accused her of crying wolf and prepared to go riding,” Andrew Morton wrote in his 1992 book, Diana: Her True Story, whose primary source was later revealed to be Diana herself.

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