LONDON — Prince Harry delighted audience members at a charity gala performance of "Hamilton" by appearing onstage and singing the opening line of "You'll Be Back."

In the hit hip-hop musical, the song is sung by the pompous King George III character, who was the titular Alexander Hamilton's foe during the American Revolution. The real-life George III was one of Harry's ancestors.

"Hamilton" famously mocks the British monarchy's role during the foundation of the modern United States.

"You say..."



Thank you to the cast and crew of @HamiltonWestEnd for a fantastic performance, raising awareness and funds for @Sentebale's work with children and young people affected by HIV #HamiltonLDN pic.twitter.com/M5hmjTfhEz — Kensington Palace (@KensingtonRoyal) 29 August 2018

As he appeared onstage at the Victoria Palace Theater in London's West End to thank cast, crew, and audience members following the performance, Harry crooned the song's opening "you say" line.

The prince then quipped "that's definitely not going to happen," before gesturing to the show's creator Lin-Manuel Miranda and adding: "He did try, but I said, 'no.'"

Harry attended the show with wife Meghan Markle, who is now officially known as the Duchess of Sussex, to raise funds for Sentebale, the HIV charity he co-founded with Prince Seeiso of Lesotho.

"Together you have raised a huge amount of money to change the lives of children in Botswana and Lesotho," he told the audience, before describing the performance as "spectacular."

Prince Harry and Meghan Markle, who is now known as the Duchess of Sussex, meet the cast and crew of "Hamilton" in London on Wednesday. WPA Pool / Getty Images

The royal couple held a meet-and-greet session to congratulate the cast after the theater had emptied.

Quote-tweeting a post from the official Kensington Palace account, Miranda said: "King George III’s great-great-great-great-great-great grandson The Duke Of Sussex sang a few bars tonight."

Prior to the performance, Miranda — who sat next to the royal couple — said it would be "fun and surreal" to see them watching his musical, according to NBC News' U.K. partner ITV News.

Speaking to reporters after meeting the prince earlier in the evening, Miranda commented: “You don’t often get a direct descendant” to watch the show.