Rocking a tux, the prince was led to the stage by Swift late Tuesday night at Kensington Palace. Once in front of the mic, he clapped his hands and nodded his head to the music as those in the crowd hollered the chorus. At times he even managed to harmonize with Swift and Bon Jovi – and play air guitar.
The impromptu concert was described by William's aides as completely "off the cuff," and as it concluded, William and Swift high-fived each another, while Bon Jovi, who was awarded the Great Britain Youth Inspiration Award in honor of his Soul Foundation, gave his royal backup singer a big hug.
The Winter Whites Gala to raise money for one of William's favorite charities, the homeless youth organization Centrepoint, began with a reception at the state apartments of the palace where William lives with Kate and Prince George and continued with a private dinner for VIPs at the Orangery on the grounds.
Earlier, Swift performed acoustic versions of her hits "Trouble," "15" and "Love Story," with its tale of princes and princesses.
As were the others, including Hollywood scriptwriter and producer Danielle Alexandra, whose movie experience helped her create a Doctor Zhivago-themed wonderland in the palace.
"There is a heartfelt reason behind this," she said, "for the homeless young people."