In a surprising twist, Prince William and Kate Middleton paid homage to the classic musical 'Grease' during their royal wedding.

Their wedding day surprise, which is still being discussed, was a special moment for Prince William and Kate Middleton.

The royal couple's wedding in 2011 was one of the most-watched in history, but after the cameras stopped rolling, they let loose and danced like Danny and Sandy.

Prince William and Kate had a surprise planned for the evening's finale, as revealed in Robert Jobson's new biography, "Catherine, the Princess of Wales," according to People magazine.

William and Catherine stood hand in hand on the dance floor, grinning, before the song "You're the One That I Want" from "Grease" began playing loudly. They then started dancing around, pointing at each other, and mouthing the words in the style of Danny and Sandy.

"It brought the house down."

Jobson's book reports that 1,900 guests attended the wedding ceremony, but only 650 guests made it to the reception hosted by Queen Elizabeth II, while the reception hosted by the former Prince Charles had 300 guests. Additionally, Jobson notes that there was a live band led by Ellie Goulding, one of the couple's favorite artists, at the reception.

The couple's first dance was serenaded by the singer with a rendition of Elton John's "Your Song," followed by her hit "Starry Eyed" and a cover of "Mr. Brightside" by The Killers, one of their favorites.

"Goulding remembered feeling extremely nervous, with trembling hands."

Since their time as students at the University of St Andrews in the fall of 2001, the Prince and Princess of Wales have made significant progress.

According to People, it was an open secret among the student community that Jobson and his partner were a couple.

Jobson stated that they strolled to class together, perused the nearby grocery store, or spent evenings at home listening to music.

A body language expert claims that Prince William and Kate Middleton are deeply in love, based on their nonverbal cues.

Until a dinner party with friends attended by Carly Massy-Birch, William's budding romance remained shrouded in secrecy, according to Jobson.

According to Jobson, the partygoers engaged in the drinking game "Never Have I Ever," where they confessed to different experiences.

The couple invited several exes to their wedding, but there were no hard feelings.

"Perhaps unwittingly, Carly exposed William’s secret love affair with Catherine, much to the prince’s chagrin." — Robert Jobson, author of "Catherine, the Princess of Wales."

The same individuals who were invited to the event included Williams' first love, Arabella Musgrave, as well as Jecca Craig, Olivia Hunt, and Massy-Birch. Additionally, Kate's exes, Rupert Finch and William Marks, were also present.

In their 2010 engagement interview, William revealed that he and Kate shared an apartment as roommates.

"We started living together as friends and it gradually evolved into a romantic relationship," William stated. "We shared an apartment with a few other people, but as we spent more time together, our bond grew stronger."