Prince Charles would not have courted Princess Diana had his second cousin said yes to his marriage proposal.

The Prince of Wales had his eyes set on Amanda Knatchbull before he married Lady Diana Spencer and Camilla, the Duchess of Cornwall. She is the granddaughter of Prince Philip's maternal uncle, Louis Francis Albert Victor Nicholas Mountbatten, 1st Earl Mountbatten of Burma.

According to the Channel 4 documentary "The Royal House of Windsor," Lord Mountbatten tried to set Prince Charles up with his granddaughter. "For years, Mountbatten was secretly lining Amanda up as a future queen" as she was considered the "perfect candidate" for her distant cousin.

Amanda, who is nine years younger than Prince Charles, grew close to the royal. Royal author Robert Lacey, in his book "Battle of Brothers," shared that the future king was actually "very fond" of his cousin and that "over the two years" they "did grow close.

It is understood that they even went on a trip to Eleuthera in the Caribbean together aboard the Royal Yacht Britannia. It was reportedly during their holiday that he asked her to marry him. Lacey said Lord Mountbatten pressured Prince Charles to propose to Amanda. He eventually asked her to marry him in the summer of 1979 before the earl's assassination by the IRA.

Unfortunately, she said no. The documentary claimed that the pair may not have had any romantic feelings for one another as Lord Mountbatten had hoped.

"They'd been together a lot, and I think that actually, the relationship was too close. They were like brother and sister," the narrator said as quoted by Mirror.

Meanwhile, Lacey said Amanda said no to Prince Charles' marriage proposal because she did not want to be in the "system." She valued her independence and considered marrying into the royal family a loss of independence. The Prince of Wales ultimately proposed to Princess Diana. They married in 1981 and divorced in 1986. He is now married to Camilla, the Duchess of Cornwall.

Amanda married author Charles Vincent Ellingworth in 1987. She is now known as Lady Ellingworth. Despite not ending up together, she and Prince Charles developed "a mutual respect and friendship that has lasted to the present day."

Princess Diana
24 February 1981: Lady Diana Spencer reveals her sapphire and diamond engagement ring as she and Prince Charles pose for photos in the grounds of Buckingham Palace following the announcement of their engagement Tim Graham/Getty Images