Long before your Meghan Markles and Kate Middletons, the royals were encouraged to marry blue-blooded aristocrats.
Enter the Spencers – one of England's most revered family dynasties with long-standing ties to the royals.
And as it turns out, Princess Diana's oldest sister, Lady Sarah McCorquodale, dated Prince Charles for nine months in 1977.
Nothing like an older sibling to pave the way for the next generation!
While their relationship ended up being pretty innocent, it's still a rather unnerving series of events and understandably a potentially explosive plot line that may be explored in the fourth season of The Crown.
Their short-lived romance came crashing down after Sarah gave an embarrassing interview about the Prince.
"Our relationship is totally platonic. I think of him as the big brother I never had. I wouldn't marry a man I didn't love, whether it was a dustman or the King of England," she boldly proclaimed to two journalists.
"If he asked me I would turn him down," she quipped.
As legend has it, bachelor Charles flipped his royal lid when he read her comments and fumed: "You have just done something incredibly stupid."
According to Princess Diana's biographer, Andrew Morton, the then 16-year-old didn't look twice at her sister's 29-year-old beau and her first thoughts about Charles were that he was a "sad man."
A prophetic sign of things to come, perhaps?
Looking back on Sarah and Charles' romance, Di reflected: "My sister was all over him like a bad rash and I thought, 'God, he must really hate that.' I kept out of the way. I remember being a fat, podgy, no makeup, un-smart lady but I made a lot of noise and he liked that."
As fate would have it, Lady Sarah ended up being the one to formally introduce her little sister to her future husband.
"I introduced them. I'm cupid," she reportedly told The Guardian after Charles and Diana announced their engagement in 1981.
Three years after Diana's first encounter with the Prince of Wales, their romance took off when they bonded over Charles' grief after losing his beloved uncle and mentor Lord Mountbatten, who had been assassinated by the IRA, at a barbecue at mutual friend Philip de Pass's estate in Sussex.
According to Diana, the two had met only 12 times before their wedding and barely knew one another before they agreed to get engaged.
Sarah would go on to marry Neil McCorquodale in 1980 and the pair share three children together.