Prince William’s university romance with then-Kate Middleton was confirmed in a surprising way – and it was completely out of their control.

The royal couple first met at St Andrews University in 2001 when they were both students. Describing their first interaction, Kate told William in their engagement interview:

“Well I actually think I went bright red when I met you and sort of scuttled off, feeling very shy about meeting you.

“Actually, William wasn’t there for quite a bit of the time initially, he wasn’t there for Freshers Week, so it did take a bit of time for us to get to know each other but we did become very close friends from quite early on.”

That friendship went on to turn romantic, with Kate reportedly catching William’s eye when she modelled a semi-sheer dress at a charity fashion show in 2002.

That same year, the pair started living together, along with two classmates. And, according to royal author Robert Jobson in his new biography Catherine, the Princess of Wales, “among the student community, it was an open secret that they were a couple”.

But it was one of William’s ex-girlfriends who officially outed the pair. According to Jobson, there was a “revealing moment” at a dinner party attended by friends of William and Kate, including his ex Carly Massy-Birch. Massy-Birch, “perhaps unwittingly” exposed William’s secret love affair with Catherine during a boozy game of ‘Never Have I Ever’, “much to the prince’s chagrin,” Jobson claims.

He cited the work of another royal author, Katie Nicholl, who also wrote about the big night in her 2013 book Kate: The Future Queen. A guest at the party told Nicholl: “[Carly] announced, ‘I’ve never dated two people in this room’, knowing full well that William was the only one who had because Kate was sitting next to him.”

According to that guest, everyone at the dinner was “in shock”. Prince William, they added, “shot a thunderous look” at his ex and reportedly whispered under his breath, “I can’t believe you just said that.” “We knew they were together, but it was the first time William confirmed his and Kate’s relationship in public,” the source said.

Happily, any feelings of ill will the Prince might have had towards Carly didn’t last. She was one of the lucky guests invited to William and Kate’s wedding in April 2011. Carly later spoke to Nicholl about her brief romance with the heir-to-the-throne. The pair dated for less than two months shortly after he arrived at St Andrews. “We got on well, but I think we would have got on well even if nothing had been going on romantically,” she said. “It was very much a university thing, just a regular university romance.”