The woman Prince Charles proposed to before Princess Diana.

At 70 years old, Prince Charles is happily married to his second wife Camilla and spending time with his grandchildren while preparing for his future role as King.

But in 1979 he was contemplating a future with a very different woman by his side.

Before he began dating Lady Diana Spencer in early 1980, Prince Charles proposed to another woman, according to various sources over the years – including most recently British documentary series The Royal House of Windsor.

That woman turned him down.

Her name was Lady Amanda Knatchbull (she’s now married and become Amanda Ellingworth) and she’s the granddaughter of Prince Charles’ “honorary grandfather” Lord Louis Mountbatten.

Lord Mountbatten, who was Prince Philip's uncle and Queen Elizabeth's distant cousin, was, in fact, the architect of the match, attempting to persuade the prince to marry his granddaughter.

According to Penny Junor's book The Firm, Lord Mountbatten began his ploy in 1974, sending a letter to his the 25-year-old great-nephew on advice about choosing a wife.

"In a case like yours, the man should sow his wild oats and have as many affairs as he can before settling down, but for a wife, he should choose a suitable, attractive, and sweet-charactered girl before she has met anyone else she might fall for," he wrote.

Yes, that sounds a lot like the description of his future wife Princess Diana who was a 19-year-old virgin when they became engaged.

But it also matched the description of Amanda, who was then 17 (and yes, Prince Charles cousin, but that never stopped royals before.)

Prince Charles was considering the prospective match and began visiting Amanda with her family occasionally, even holidaying with them in the Bahamas in 1977.

Then during another trip in 1979 aboard a ship in the Western Isles off the coast of Scotland, Charles proposed to Amanda.

According to The Royal House of Windsor, the conversation went something like Charles turning to ask "Will you be my wife?" and her telling him "no".

There are many reasons suspected for her declining the proposal. One is that their time spent together felt more familiar to Amanda than Charles would have liked and she turned him down because he was more like a brother to her.

Another is that she feared for her own life, as the IRA was terrorising the English at the time. Prince Charles proposal came around the time her grandfather, Lord Mountbatten, was assassinated by the Irish Republican Army (IRA) in August that year. Amanda's grandmother, Lady Brabourne, and youngest brother Nicholas were also killed in the attack.

Prince Charles seemed to be on a mission to settle down, beginning dating Diana - who he had met a few years earlier - in January the following year.

And in February 1981 when he proposed, she said yes.