King Charles and Queen Camilla have been happily married since April 2005, but it was an “infuriating social incident” that finally persuaded the now-King to propose to his wife.

Royal author Tina Brown claimed in her book The Palace Papers that many of the royals had been invited to the wedding of Edward Van Cutsem and the Duke of Westminster’s daughter, but it was the seating plan that particularly upset Camilla.

Ms Brown wrote: “Charles and Camilla were apprised of the seating plans the weekend before the wedding. The arrangements revealed Mrs Parker Bowles to be relegated to the social margins of the event.”

Camilla had been expected to sit directly behind Charles, as they were not married, but “that “Dutch Cow” as (Camilla reportedly called [mother of the groom] Emilie Van Cutsem, had stuck her on the other side of the cathedral with the bride’s friends.

She was reportedly placed at the back and told that she could not enter or leave by the main door.” A courtier told the Daily Mail at the time that this had “sent Camilla over the edge”.

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Mrs Van Cutsem however refused to back down, claiming she was sticking to protocol, but Ms Brown explained that Camilla would not be “understanding”.

The author wrote: “She would not be humiliated in front of all of Charles’s snotty circle and, more importantly, the Royal Family.

“The Prince had to choose between attending the wedding without her or snubbing his closest friends and his godson. It was Camilla’s line in the sand.”

Conveniently enough Charles was unable to attend the wedding due to a prior commitment to visit the barracks at Warminster in Wiltshire to meet the families of soldiers from the Black Watch.

Royal biographer Penny Junor wrote in her book The Duchess: The Untold Story that Camilla’s father Major Bruce Shand was the one who persuaded the then-Prince of Wales to act.

Ms Junor said: “Although he loved the Prince dearly, he thought him weak and was worried about how vulnerable he had made Camilla by allowing her to live in limbo.