Meet the woman Kate Middleton was rumoured to be jealous of.

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Look, I’ll be the first to admit that in past relationships, certain names popped up from time-to-time that made me feel uncomfortable.

While I never really had a legitimate reason to be jealous, I couldn’t help but feel a pang whenever my boyfriend’s ex-flame (a model who was also studying medicine) liked his Instagram photos or showed up at parties through mutual friends.

Well, it turns out I’m not alone – even the Duchess of Cambridge isn’t immune to jealousy.

It’s hard to imagine anyone Kate Middleton could possibly be jealous of, but apparently, years before they wed – there was one woman in Prince William’s life who gave her a touch of the green-eyed monster.

And there’s one very big reason why.

The woman in question is Isabella Calthorpe, a British heiress with several ties to the royal family.

Her half-sister Cressida Bonas, one of her four half-siblings and two full, dated Will's brother Prince Harry from 2012 - 2014, and she's close friends with Princess Beatrice and Princess Eugenie.

She's now married to Sir Richard Branson's son Sam Branson, but there was a time when she was widely known as Prince William's crush.

According to royal expert and author Katie Nicholl, who wrote William and Harry: Behind the Palace Walls, Prince William had tried, unsuccessfully, to court Isabella on a few occasions.

Apparently, according to the author, his crush may have even contributed to Will and Kate's decision to take a break in 2007.

Oh.

A royal source told the Daily Mail in 2007 he had visited Isabella's family home in London to spend time with her around the same time the break occurred:

"He had fallen for her in a huge way and wanted to be with her. He propositioned her several times that summer and although Isabella was single, she knocked William back and said it would be too damaging for her and her career," the source said of the summer of Will and Kate's break.

"She is a name in her own right and on her way to becoming hugely successful. In her view, being affiliated with William in a girlfriend capacity would be damaging for her."

Another source added fuel to the rumour in 2007, telling the publication they thought William had actually decided to initiate his break with Kate to pursue Isabella.

"Isabella was very much on the scene that summer," the source said.

"I would go so far as to say that William dumped Kate because he thought he had a chance with Isabella and Kate knew that. Kate's a tough cookie, though, and stood aside and waited for William to come back to her which eventually he did. Before that, though, he did everything he could to woo Isabella."

They added:

"William was madly in love with her but when he knew there was no chance of them getting together he went back to Kate. Kate was very aware of his obsession with Isabella and she was incredibly threatened by her. Isabella is drop-dead beautiful and would leave any girl in the shade. Kate accepted William back again but on the condition that he would not speak to Isabella again."

Wow.

In Nicholl's book, she also claimed Kate had banned Will from contacting Isabella when they got back together that year.

"It was obviously the break that William needed, and by Christmas they were back together again, although Kate had a condition. Word had reached her of William’s visits to Isabella, and Kate insisted that William was not to contact her again."

...We're not sure we believe all that. Isabella was still invited to Will and Kate's royal wedding in 2011, so there seems to be no bad blood between them.