The Royal couple headed to Victoria in London last night to see a special performance of Hamilton’s West End show.
Afterwards Prince Harry took to the stage with the cast, crew and show creator Lin-Manuel Miranda to say thank you.
But before his speech, The Duke of Sussex began to sing You’ll Be Back, which is performed by King George III in the show.
The monarch is the prince’s great-great-great-great-great-great grandfather who ruled for 60 years and saw America declare independence from the British Empire.
Sadly Harry only managed to get the first two words of the song out – “You say…” – before audience and cast applauded him.
Miranda even stomped his foot in amusement at the moment, which was posted on Twitter by Kensington Palace.
Michael Jibson, who plays King George in Hamilton later tweeted: “The moment I was upstaged.”
Last night’s Hamilton performance was in aide of Sentebale, a charity the Prince founded to help children and young people in Lesotho and Botswana who are affected by HIV.
After the musical start to his speech, Harry said: “Ladies and gentleman, thank you so much — thank you to Cameron Mackintosh productions, to the show’s creators Thomas Kail and of course Lin-Manuel Miranda, the cast and crew.
“And as already mentioned, a round of applause for yourselves for taking part in this evening’s activities because you have together, raised a huge amount of money to change the lives of thousands of children in Botswana.
“Through that work that we’re going to be doing now– we will be able to stop the generational hand down of the stigma around HIV.”
Seeing Hamilton last night wasn’t the first time for Meghan though
The Duchess of Sussex saw Hamilton in New York with Priyanka Chopra months before marrying Harry.
Meanwhile the Royal couple viewed a performance of the West End version back in February, while on a date night.
Hamilton is a multi-award winning hip-hop musical based on the life of American founding father Alexander Hamilton.