Sounds like he's trying to make up for it now.
The "Faith" singer tweeted on Sunday that he'd been "thinking about Will and Kate," and recounted the incident when young William asked him to sing with "Uncle Elton [John]" at a Kensington Palace Christmas party. But Michael said he was "too shy" to perform in such an intimate setting.
"So I said no...it was excruciating, his little Xmas smile disappeared, but the only people I knew in the room were Diana and Elton!"
He later tweeted: "So I bloody said no to the future king of my country..."
So now the singer is working on a very personal "wedding pressie" to William and his bride-to-be Kate Middleton: a song recorded just for them. Michael said that he's not angling for an invite, but singing because he's happy for them.
Rejecting his own songs as "too sad," Michael asked his Twitter followers to send him cover song suggestions.
"Remember twitterville, this has got to be a romantic, OPTIMISTIC song for two good poeple. Who happen to be royalty....:)" he wrote.
Yesterday Michael said he may have found the winner. He described it as a "beautiful song" that is a "perfect fit" for the duo and hopes to have it completed by the end of the week—barring TMI breaks.
Michael wrote, "I'm so happy for William, I only ever met him twice, but he was such a nice kid..."
Let's hope the Prince remembers the meeting with the pop star just as fondly.
Also giving her thoughts on royal-to-be Kate was Harry Potter star Emma Watson, who said she has sympathy for the future Queen of England.
"Poor girl, that must be an incredible amount of pressure," Watson said about the preparations for the big day in a recent interview. "I hope she's enjoying it. Must be intense."