They were once arch nemeses of the highest order!

Indeed, one of the most well-documented rivalries in history was between Princess Diana and Camilla Parker Bowles. During the Princess of Wales' relationship to then-Prince Charles, the beloved royal famously said, "There were three of us in the marriage."

Of course Diana is tragically no longer with us, and Camilla has stepped into the role of wife to now-King Charles. That turn of events would have been impossible to imagine years ago, and yet, here we are.

Now, consider an even more unthinkable twist of fate: Are Princess Diana and Camilla actually related in some way?

So, are Princess Diana and Camilla related?

It may not come as a huge surprise that the royal family is actually quite a small circle.

Did you know, for instance, that according to Express, the late Queen Elizabeth II and her husband of three-quarters of a century, the late Prince Philip, were related? Indeed, the former heads of the British royal family were cousins, descended from Queen Victoria, as well as King Christian IX of Denmark, making them cousins twice over!

Meanwhile, King Charles and Queen Consort Camilla, who married in 2005, are also related. They are ninth cousins once removed via the family line of Henry Cavendish, the 2nd Duke of Newcastle, per Express.

And yes, Diana and Camilla are also related! See, small world, right? So how are they related? Well, both of the monarch's wives are descended from Charles II, who ruled in the 17th century.

Adding to the seemingly-small family tree intrigue of the royal family is that Diana, too, was related to Charles!

They are seventh cousins once removed via the relative William Cavendish, 3rd Duke of Devonshire.

Are Prince William and Kate Middleton related?

To review, Queen Elizabeth and her husband were related. King Charles is related to both Diana and Camilla. Diana and Camilla are related to one another.

That leads to the next natural question of whether the future King of England, Prince William, is related in some way to his wife, Kate Middleton?

Well, again, not surprisingly, the answer is "yes."

William and Kate are fourteenth cousins once removed. Here's how, according to Patrick Cracroft-Brennan, from Cracroft’s Peerage: “Her great-great-grandmother, Frances Elizabeth Greenhow, was the 10 x great-granddaughter of Sir William Gascoigne, a Yorkshire knight who died in 1487. He married Lady Margaret Percy, 4th and youngest daughter of Henry Percy, Earl of Northumberland."

“The Earl descended from King Edward III through both his parents. Prince Charles and the late Princess Diana both descend from Sir William Gascoigne and his wife Lady Margaret," the source continues.

And so, “This makes William and Kate fourteenth cousins once removed through his mother and fifteenth cousins through his father."

At end of all of this, in case you're wondering what it means to be once removed, it's when your cousin has a child, and that child becomes your cousin, once removed, per My Heritage.