Prince William and Kate Middleton have been married for more than eight years, and fans of the royal family often believe they know all about the couple’s love story. However, a royal biographer revealed the Duke and Duchess of Cambridge managed to keep a major secret from the world at the start of their relationship.

William and Kate met in the early 2000s while attending St Andrews University, and began dating shortly after. Although stories about the couple’s relationship made international headlines, there was a time when few knew about their romance.

In the 2011 book “William and Kate: A Royal Love Story,” Christopher Anderson claimed Prince William went to great lengths to secretly attend Kate’s birthday celebration. “Kate celebrated her 21st birthday that January 2003 with a small family party at home in Bucklebury,” the author revealed.

“William had slipped quietly out of London, and now he was meeting Kate’s dazed, but not entirely surprised, parents for the first time. He told them, ‘I wouldn’t have missed the chance to sing Happy Birthday to Kate for the world.’”

At the time of Prince William’s romantic surprise, Anderson claimed their relationship was a well-kept secret. “Even at St Andrews, only a handful of students knew that William and Kate were in the throes of a deepening love affair,” the royal biographer wrote.

Although Prince William and Kate were passionate about their blossoming romance, the Duke of Cambridge’s friends didn’t approve of the woman, who would eventually become his wife.

In a 2008 Vanity Fair article, author Vicky Ward claimed Prince William’s friends did not make Kate feel welcomed in their exclusive circle.

“There are plenty of snobbish insults from people who, despite Middleton’s obvious attributes, believe that the monarchy needs to stop marrying ‘out’ of its class,” she revealed.

Despite his friends’ disapproval, the royal saw a future with his college sweetheart. Prince William and Kate married in 2011, and are now parents to Prince George, Princess Charlotte and Prince Louis.

Prince William and Kate Middleton
Britain's Prince William and Kate Middleton are pictured on a five-day visit to Pakistan. AFP/Aamir QURESHI