Prince Charles and Camilla Parker Bowles (opens in new tab) have come a long way in their happy marriage, but Prince Charles actually knew she was his "soul mate" before either married the other.

According to royal biographer Robert Lacey in his book Battle of Brothers: William and Harry - The Inside Story of a Family in Tumult (opens in new tab)), Prince Charles eventually found out in 1972 According to the book, Prince Charles ultimately identified the weekend he spent with Camilla in December 1972 as the moment he realized that she was the one for him.

It was December 1972, and Charles was to sail (opens in new tab) with the Royal Navy to the Caribbean in the New Year. Before setting sail, Charles took Camilla to Portsmouth to see the ship on which he was to sail. As Prince Charles wrote in a plaintive letter to Lord Mountbatten, "This was the last time I would see her for eight months."

According to Lacey, it took 35 years, but Charles eventually pointed to that last weekend as "the moment when I first became convinced that I wanted to marry Camilla and that she was my soul mate for life." But he did not have the courage to tell her properly or strongly."

That mistake would have a profound impact on Charles and Camilla's lives (opens in new tab), and by March 1973 she was engaged to her first husband, Andrew Parker Bowles (opens in new tab).

"Charles declared his love, but did not make a move. He whispered sweet nothings, but said nothing substantial. Giles Brandreth, author of "Charles and Camilla: A Portrait of a Love Affair" (opens in new tab), wrote in 2005. Sometimes the actions we do not take really matter more than the actions we do take."

Charles and Camilla infamously returned to each other after having an affair when Charles was still married to his first wife, Princess Diana. They eventually married in 2005.