Royal biographer Robert Jobson’s new book reveals a surprise the future Prince and Princess of Wales had up their sleeves for their unsuspecting guests.

Kate Middleton and Prince William’s April 29, 2011 nuptials were one of the most watched royal weddings of all time, but after their televised ceremony at Westminster Abbey and double kiss on the Buckingham Palace balcony, there were parts of the day the public didn’t see.

Although there were 1,900 guests in attendance at the ceremony, far fewer made the cut for their two wedding receptions that followed: one hosted by Queen Elizabeth for 650 guests and a second hosted for 300 by the groom’s father, Prince Charles (now King Charles).

The latter, smaller reception was held in the Throne Room of Buckingham Palace, and in his new book Catherine, the Princess of Wales, royal biographer Robert Jobson said one guest described the evening’s celebrations as “the most magical party imaginable.”

Only William and Kate’s closest inner circle of friends were invited, Jobson writes, and a live band led by Ellie Goulding, one of the couple’s favorite artists, led the entertainment for the evening. Goulding sang Elton John’s “Your Song” to mark their first dance, and afterward, Goulding called the experience “scary”: “I was so nervous,” she said, per Jobson’s book. “My hands were shaking.”

After performing “Your Song,” Goulding performed several more selections, including her hit “Starry Eyed” and a cover version of “Mr. Brightside” by The Killers—another of William and Kate’s favorites, Jobson writes. PEOPLE previously reported that the newly minted Duke and Duchess of Cambridge also sang and danced to The Beatles’ “She Loves You” before fireworks capped off the evening.

“William and Kate were in the middle, giving it their all,” a guest told PEOPLE back in 2011. “They really went for it. They were in the full party spirit and stayed until the last minute.”

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For the evening’s finale, Prince William and Kate had a special surprise up their sleeves, Jobson reveals in Catherine, the Princess of Wales: “They stood holding hands in the middle of the dance floor grinning, then suddenly the opening bars of the song ‘You’re the One That I Want’ from the musical Grease came booming out,” Jobson writes. “William and Catherine then began dancing around, pointing at each other, and mouthing the words with the style of the lead characters Danny and Sandy. It brought the house down.”

PEOPLE reported back in 2011 that guests were then asked to go out to the fine lawns behind the palace for another surprise. There, a Fiat, a classic Cinquecento model, had been decked out with “balloons all over it and an open top,” a guest said. “They squeezed into it, sat out on the roof, while one of the servants drove the car and drove off along the gravel paths. Then the fireworks went off. There were big ones, but it was only for two minutes.”

While Prince William and Kate drove away, they didn’t actually leave the premises, PEOPLE reported, and as their guests left at 3 a.m., it left “the newlyweds as the only guests at the palace,” Jobson continues.