The new dad had asked his grandmother, the Queen, for permission to hold the first-ever soccer game at the palace to celebrate the Football Association's 150th anniversary.
"I cannot tell you how excited I am that later today we will be playing football on my grandmother's lawn," he said in his speech opening the event at Buckingham Palace on Monday. "One warning, though: If anyone breaks a window, you can answer to her."
The Queen was unable to attend the event, but William said that there was "one small silver lining" in that: there wouldn't be any corgis running onto the pitch.
Wearing bright orange shoes, William – who's president of the Football Association – laughed as he trained with members of the royal household's football team.
Two of England's oldest amateur teams – Civil Service FC and Polytechnic FC – played a game during the event, and during half-time, they were treated to oranges and drinks, brought out on silver platters by the Queen's footmen.
Can't get enough about the royal baby? Be among the first to know the news! Sign upbelow for our daily newsletter to find out about the new addition and otherspecial offers – so you'll be the first to know everything about Prince George and how the new mom and dad are adjusting to parenting.