Prince William reportedly had a ‘thunderous’ response when his ex exposed his romance with Kate Middleton.

Prince William and Kate Middleton may have a fairytale romance for the ages, but the future king was reportedly left upset when their romance was exposed during the early days of their relationship. After the couple first met and sparked romance in the halls of St. Andrews when they were both students, royal author Robert Jobson revealed that they were reportedly keeping things low key until once of William’s exes revealed they were an item.

Jobson wrote in his new book, Catherine, the Princess of Wales, per the Mirror, that “it was an open secret, among the student community, that Kate and William were a couple.” However, it was one of William’s ex-girlfriends, Carly Massy-Birch, who “perhaps unwittingly” outed their relationship during a “revealing moment” at a dinner party attended by friends of the couple during a booze-filled game of “Never Have I Ever.”

Citing royal author Katie Nicholl, who wrote about the night in her 2013 book Kate: The Future Queen, Jobson claimed that a guest told Nicholl that Massy-Birch “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,” and William “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 added.

While William may not have been ready to go public with their relationship just yet, it didn’t seem to have much of an impact on his relationship with Kate. Although the couple briefly split in 2007 – William later told TV News’s Tom Bradby, “we did split up for a bit, but that was just, we were both very young, it was at university, and we were both sort of defining ourselves as such and being different characters and stuff. It was very much trying to find our own way and we were growing up.” – they quickly reunited, and in October 2010, William dropped to one knee and popped the question, William and Kate announcing their engagement the following month. The couple went on to tie the knot at Westminster Abbey in London on April 29, 2011.

William and Kate have now settled into royal life together, one that now includes the happy title of “mom” and “dad” to Prince George, 11, Princess Charlotte, 9, and Prince Louis, 6. The youngsters take up the respective second, third, and fourth spots in the British line of succession after their father, who moved to the No. 1 placement when his father King Charles ascended the throne.