Prince Charles [Courtesy]

We all know the story of Prince Charles and Princess Diana, we followed their romance, all the ups and downs until the very end.

And after that, we watched as the Prince of Wales married his long-term love, Camilla Parker-Bowles.

But did you know that Charles is said to have also once proposed marriage to another woman, Amanda Knatchbull, before his relationships with either of these two ladies?

However, things didn't quite go to plan as it turned out she wasn't actually interested in him that way. Ouch.

This is according to a Channel 4 documentary called The Royal House of Windsor, in which it is claimed Charles' 'honorary grandfather,' Lord Mountbatten attempted to set the prince up with his granddaughter, Amanda.

At nine years his junior and despite being a distant cousin of his, Amanda was considered "the perfect candidate" for Charles.

"For years, Mountbatten was secretly lining Amanda up as a future queen," explained the programme's narrator.

Charles is said to have also once proposed marriage to Amanda Knatchbull. [Courtesy]

And it seemed as if love was destined to blossom between the two, with the show detailing how Charles once took Amanda on the Royal Yacht Britannia for a trip to Eleuthera in the Caribbean.

This was back in 1977 and it is thought that during this holiday, he popped the question.

"Charles turned to her and says, 'Will you be my wife?' - and she said no," the narrator says.

They added: "They'd been together a lot, and I think that actually, the relationship was too close.

"They were like brother and sister."

Not long after this, Charles began to court Lady Diana Spencer and as we all know, when he asked her to marry him, she said yes.

The late Princess Diana [Courtesy]

They were married in 1981 and divorced in 1996. Charles later went on to marry Camilla, The Duchess of Cornwall in 2005.

Meanwhile, Amanda married author Charles Vincent Ellingworth in 1987 and the pair have three children together.

Today she is known as Lady Ellingworth and has made some brilliant contributions to British social work.