Before he married Princess Diana , Prince Charles dated Camilla and was said to be completely in love.
It's been widely reported that the Royal Family didn't think she was a suitable bride for the heir to the throne, and he was put under pressure to end their relationship and find someone else.
The couple were forced to take a break when the 24-year-old Charles went on a tour with the Royal Navy.
During his time away he received a letter from Camilla which broke his heart, and he thought was cruel.
In the letter, Camilla revealed she had accepted a wedding proposal from her boyfriend Andrew Parker Bowles.
Royal author Penny Junor wrote about the letter in her book about Camilla, The Duchess: The Untold Story .
She states: "She wrote to Charles herself to tell him. It broke his heart."
Penny claims the devastated prince shared his heartbreak in letter to his friends and family.
She writes: "He fired off anguished letters to his nearest and dearest.
"It seemed to him particularly 'cruel', he wrote in one letter, that after 'such a blissful, peaceful and mutually happy relationship' fate had decreed that it should only last a mere six months."
Camilla married Andrew in 1973 and the couple went on to have two children. They divorced in 1995.
Charles and Camilla married in a civil ceremony at Windsor Guildhall in April 2005. The wedding was attended by the Royal Family, including the Queen and Princes William and Harry, and Camilla's family.
