Britain's Prince Charles' relationship with then-Camilla Parker Bowles when he was married to Princess Diana remains still fresh for many. However, even before he proposed Diana, the British throne's heir apparent was encouraged to ask his cousin Amanda Knatchbull for her hand in marriage but she 'refused'.

Knatchbull is the granddaughter of Lord Mountbatten, who was Prince Philip's maternal uncle. This made her Charles' second cousin. Mountbatten sought Charles to marry Knatchbull and the prince was admittedly "very fond" of her, according to royal author Robert Lacey.

Amanda Knatchbull
Amanda Knatchbull Twitter

"Over the years the two cousins did grow close, developing a mutual respect and friendship that has lasted to the present day," Lacey wrote in his book "Battle of Brothers," according to the Express.

However, when Charles proposed Knatchbull in the summer of 1979, shortly before Mountbatten was assassinated by the Irish Republican Army, she politely turned down his proposal, Lacey wrote. The reason? She was "independent-minded."

"'The surrender of self to a system,' she explained, was so absolute when joining the royal family, it involved a loss of independence 'far greater than matrimony usually invites'," Lacey wrote.

Moreover, Knatchbull saw her relationship with Charles more that of a brother and sister's and that they were too close. She went on to marry author and property entrepreneur Charles Vincent Ellingworth in 1987. They are parents to three sons.

Prince Charles and Lady Diana
Britain's Prince Charles and his then-fiancé Lady Diana exchange a private word during her first 'walkabout' in Tetbury, Gloucestershire, the United Kingdom, on May 22, 1981. Flickr/Joe Haupt

In 1981, Charles asked Diana to marry him and received a positive response. The two married the same year, but they grew apart within five years of their marriage due to their 13-year age difference, incompatibility and extramarital affairs.

Charles rekindled his relationship with former girlfriend Camilla in 1986. In 1994, the Prince of Wales admitted to infidelity and said he resumed his relationship with Camilla only after his marriage with Diana was "irretrievably broken down, us both having tried." Eight years after Diana's death in a car crash in Paris, Charles married Camilla in a civil ceremony in 2005. She is now the Duchess of Cornwall.

Prince Charles and Camilla Parker
Britain's Prince Charles and Camilla, Duchess of Cornwall, chat at Turangawaewae Marae in Ngaruawahia, south of Auckland, New Zealand Nov. 8, 2015. Reuters