Following their marriage in May of 1960, Princess Margaret and Lord Snowdon were known as Britain's most glamorous couple, but their love story wasn't always a joyful one.

Snowdon, then Antony Armstrong-Jones, was the first "commoner" to wed a king's daughter in over 400 years, but rumors of a rift in the marriage began as early as 1967. By the 1970s, the famous royal couple had drifted apart and in 1978, after almost 20 years of marriage, they announced their divorce.

Princess Margaret and Antony Armstrong-Jones on the day they announced their engagement, February 1960. Getty Images

Here's the history behind the Princess and the photographer's whirlwind love, a story which has become well known through its depiction in the Netflix series The Crown.

1. Their relationship was a well-kept secret.

After the sad end of her relationship with Captain Peter Townsend, the young Princess was known as one of the most desirable single women in England. As Anne de Courcy explains in her biography of Snowdon, the young royal was "a unique and intoxicating challenge" for the famous society photographer. When they first met at a dinner party in 1958, it didn't take long for the couple to hit it off. However, it was a few months later, when Armstrong-Jones was commissioned to photograph Margaret, that the Queen's sister started her secret love affair.

"Nobody knew about their relationship, there wasn't a whisper about it, " de Courcy told Town & Country. "She would see him in secret at his studio and yes, he would join her at parties, but no one could pinpoint which man she was in interested in. The press focused more on the ones who were seen to be eligible. They didn't think of Tony who was often in the background."

2. The couple were warned not to marry, but the royal family did approve.

Princess Margaret wanted to show the public she had moved on from Townsend, and on February 26, 1960, her engagement to her new love interest was announced. The news came as a surprise to many, and it didn't go over well with everyone, particularly royal courtiers who would have preferred Margaret marry a wealthy aristocrat.

Princess Margaret on her wedding day. Getty Images

However, the royal family were delighted with the match. "They all liked him very much—Tony had great charm, very good manners and he knew exactly how to behave," de Courcy explained. "He felt devotion to the royal family, to the Queen, who he admired immensely. He got on very well with Prince Charles and he adored the Queen Mother."

After Margaret's first unhappy love affair, the Queen wanted her sister to be happy and the public, who were pleased to see Margaret settle down, were eventually supportive too. On May 6, 1960, the couple's became the first royal marriage to be broadcast on television. According to The Daily Express, it attracted over 300 million viewers around the world.

3. The Snowdons were a popular couple, but cracks in their relationship appeared early.

After they returned from a six-week honeymoon aboard the royal yacht Britannia, the newlyweds moved into Kensington Palace. Armstrong-Jones was given the title Earl of Snowdon and in 1961, they welcomed their first child, David, into the family. Their daughter Sarah was born three years later in what was a happy time in their relationship.

"The first few years were wonderful," de Courcy said. "They had a lot in common, there was banter between them—he would help her with her speeches. They [were] very close in the first few years." However, while they both enjoyed the celebrity lifestyle, their desire to be "centre-stage" is said to have caused friction in their marriage soon after the birth of their daughter.

"They were both pretty strong-willed and accustomed to having their own way, so there were bound to be collisions," says De Courcy.

But there was more to the rift than a clash of personalities. By 1962, Snowdon had been appointed artistic advisor to The Sunday Times, a role he took seriously.

Princess Margaret with her husband Lord Snowdon and son Viscount Linley shortly after the birth of her daughter, Lady Sarah Armstrong-Jones, 1964. Getty Images

"Margaret's template of marriage was quite different from Tony's," she added. "He had parents who split, while her parents' and sister's marriage were very happy. She expected her husband to be with her more, but one of Tony's strongest motivations was work. He had a workshop in the basement of Kensington Palace, and while she was understanding of his work commitments, Margaret didn't realize it would take him away from her so much."

4. Once their marriage fell apart, both parties were unfaithful.

After Sarah's birth, there were signs the royal marriage had started to crumble. According to The Evening Standard, Snowdon started having casual flings while he was away on photographic assignments, while Margaret had a brief relationship with Snowdon's university friend Anthony Barton, and later with Roddy Llewellyn, a landscape gardener 18 years her junior. In 1969, Snowdon embarked on an extramarital affair with Lady Jacqueline Rufus-Isaacs, which despite her own infidelities, upset Margaret greatly.

Lord Snowdon, with his children David and Sarah at Windsor Castle Getty Images

"The flings used to upset her a lot," de Courcy said. "She had some too, but never as long as his. They weren't revenge affairs, she just wanted to feel desired."

After years of infidelity the couple separated in 1976. Two years later, Kensington Palace announced that the royal couple were divorcing. It was the first royal divorce since King Henry VIII's in 1540. "Her Royal Highness The Princess Margaret, Countess of Snowdon, and the Earl of Snowdon, after two years of separation, have agreed that their marriage should be formally ended. Accordingly, Her Royal Highness will start the necessary legal proceedings," the statement said.

5. The pair remained great friends.

Despite their troubles, the pair remained close until Margaret's death in 2002. "They always maintained a solid friendship, once the bitterness of the divorce was over," de Courcy says, although Snowdon's love life remained complicated.

Soon after the divorce was finalized, he married Lucy Lindsay-Hogg, the former wife of a film director, in 1978. Their only child, Lady Frances Armstrong-Jones, was born the following year, but Snowdon divorced again in 2000 after it emerged that he had fathered a son, Jasper, out of wedlock with journalist Melanie Cable-Alexander. It was later reported that he had fathered an daughter, Polly Fry, just before marrying Princess Margaret. A DNA test in 2004 apparently proved his paternity, but he denied any knowledge of the claims at the time.

On Friday January 13, 2017, Buckingham Palace confirmed the Earl had passed away at the age of 86. He will no doubt be remembered as a talented photographer, who was also a passionate campaigner for the disabled throughout his life. However, his connection to the royals will always get top billing. Antony Charles Robert Armstrong-Jones will always be known as the man who married—and divorced—the Queen's glamorous sister.

Katie Frost Senior Editor Katie Frost is Deputy News Editor in the Newsroom, covering lifestyle, travel, food, celebrity and royals-related content.

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