How Prince William and Kate Middleton's affair was revealed during a dinner party game

LONDON, UNITED KINGDOM: Kate Middleton and Prince Williams’ love affair is one-of-a-kind.

The couple met during their first year at the University of St Andrews in 2001. However, they were already dating someone else at the time.

What did Kate Middleton and Prince William enjoy the most doing during their college? 

When Kate Middleton and Prince William started dating, they didn’t go public with their new relationship, wrote royal biographer Robert Jobson in his latest book 'Catherine the Princess of Wales.'

"Among the student community, it was an open secret that they were a couple,” he mentioned.

The two used to enjoy walks to the class, explored the local grocery store and spent nights at home listening to music together.

In 2010, Prince William opened up on their time living together as roommates with a few other friends during an engagement interview, "We moved in together as friends. We lived with a couple of others, as well, and it just sort of blossomed from there, really. We just saw more of each other, hung out a bit more and did stuff."

In his new book, Jobson shared, that William and Kate's relationship "remained shrouded in secrecy,” until "a revealing moment occurred during a dinner party with friends attended by Carly Massy-Birch," an ex-girlfriend of Prince William. 

The bunch decided to play "Never Have I Ever," a drinking game during which players confess to their previous experiences, according to People.

"Perhaps unwittingly, Carly exposed Prince William’s secret love affair with Catherine, much to the prince’s chagrin," he wrote. 

Prince William's ex confronted him about his secret affair with Kate Middleton

Interestingly, another royal biographer Katie Nicholl mentioned one of the memorable night from 2002 in her book, ‘The Making of a Royal Romance.’

She wrote when it was Massy-Birch's turn, "She 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," one of the friends present at the party told Nicholl.

The guest added that everyone was “in shock” by Massy-Birch's move and that Prince William "shot a thunderous look" at her and 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.

Prince William, however, did invite Massy-Birch and his other girlfriends from the past to his wedding with Kate in 2011.