The palace apparently didn’t approve of the match from the beginning.

Prince Charles and Camilla, Duchess of Cornwall celebrated 13 years of marriage this year, but anyone who’s ever followed the royals knows that their relationship dates much further back than that.

The future king reportedly met his second wife in the summer of 1971. They immediately took to each other and jumped at every opportunity to spend time together. Yet despite their close connection, it took another three decades for the couple to wed. In between came an extramarital affair, plenty of scandal, two divorces, and a whole lot of heartbreak.

It’s tempting to wonder how history would have played out if they had simply stayed together in the beginning, but just like any break-up, it’s complicated. Multiple factors both forced the couple apart and made a potential proposal impossible at the time.

Here are five of the reasons most commonly cited by historians and royal experts why Prince Charles and Camilla Parker Bowles didn’t marry at first.

Prince Charles went overseas.

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Prince Charles attends the opening of the Prince of Wales Bastion in St Kitts in 1973 wearing his naval uniform.

Prince Charles met his second wife through a mutual friend, Chilean historian Lucia Santa Cruz. He was instantly taken with her, especially because she was “not in anyway overawed by him, not fawning or sycophantic,” royal biographer Penny Juror wrote in The Duchess: Camilla Parker Bowles and the Love Affair That Rocked the Crown.

The two met up frequently at polo matches and later snuck secret time away at Broadlands, the estate belonging to his uncle Lord Mountbatten. Their relationship had a deadline though. Prince Charles was scheduled to leave on the HMS Frigate at the beginning of 1973 with the Royal Navy.

But instead of asking Camilla to wait for his return in eight months, he reportedly refrained from expressing the strength of his feelings. His absence proved an opportunity for Camilla to reconnect with her longtime beau, Andrew Parker Bowles.

Camilla was in love with Andrew Parker Bowles.

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Camilla Shand marries Major Andrew Parker Bowles at the Guards Chapel, Wellington Barracks, on July 4, 1973.

Camilla Shand met her first husband in 1965 at her debutante party. “He was 25 and a rather beautiful officer in the Household Cavalry; she was 17 but remarkably self-assured,” Juror says. “Andrew went over to her and simply said, ‘Let’s dance.’ They danced and she fell in love.”

The couple shared an on-and-off relationship for the years that followed. Andrew was away himself with his regiment when Camilla connected with the prince. The ups and downs of their relationship also correlated with the officer’s penchant for other women. At one point, he was even seeing Princess Anne, Prince Charles’s younger sister.

According to Juror, his status as an eligible bachelor “only made him more attractive” to Camilla. Despite his well-established ways, Andrew finally proposed to his long-time girlfriend in March 1973, when Prince Charles was thousands of miles away in the West Indies. Camilla accepted the proposal and they wed the following year.

She had a “reputation.”

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Prince Charles chats with Camilla Shand in an undated photo taken at a polo match.

Even if both had professed their feelings for one another, Prince Charles and Camilla likely felt that they could never marry given royal protocol at the time. First of all, even though her maternal grandfather was a baron, Camilla did not come from a sufficiently aristocratic background to make her a serious contender for a future queen.

Secondly, deeply rooted sexism surrounding the prerequisite virginity of a royal bride doomed the match from the start. “In a case like yours, the man should sow his wild oats and have as many affairs as he can before settling down,” Lord Mountbatten wrote in a letter to Prince Charles. “But I think for a wife he should choose a suitable attractive and sweet-character girl before she has met anyone else she might fall for.”

Her dad conspired against her.

Andrew’s proposal may have stemmed from more than just romance. His brother and Camilla’s father wanted the bachelor to commit to his girlfriend of nearly seven years, so they reportedly hatched a plan.

“They intervened by publishing an engagement notice in The Times,” Sally Bedell Smith wrote in Prince Charles: The Passions and Paradoxes of an Improbable Life. “His hand publicly forced, Andrew proposed.”

Other people had plans for the prince.

Prince Charles had family members playing matchmaker too. Lord Mountbatten wanted his nephew to marry his granddaughter, Amanda Knatchball, author Carolly Erickson wrote in Lilibet: An Intimate Portrait of Elizabeth II.

Queen Elizabeth the Queen Mother made designs too. She pushed her grandson toward the granddaughters of her close friend and lady-in-waiting, Lady Ruth Fermoy. Her tactics eventually worked. Prince Charles eventually dated Lady Sarah Spencer in 1977, which is how he met her younger sister and his future bride Lady Diana Spencer. The couple began dating in 1980 and married the following year. The rest is history.