It all happened when professional comedian Jack Whitehall was sitting with the Duke and Duchess of Cambridge at a Royal Variety Performance in the royal box.
Jack casually brought up the fact that he and Kate went to the same school, but never talked to each other.
The comedian then quipped how the Duchess has always been his school crush.
Jack said at the 2014 show: “We were actually at school together. This is true. We were at the same school.
“I don’t know whether it’s appropriate given the circumstances, but you were probably my first ever crush.
“Okay, definitely inappropriate. You Highness is giving me a very sharp look,” Jack added.
This uncomfortable interaction enraged William who made a passive-aggressive remark right after.
“Because he was very nice, but very passive-aggressive, ‘Oh so you were flirting with my missus? Oh no, no, that was very, very funny’.
“That’s him going, ‘I could have you beheaded,’” Jack later recalled of the Duke reprimanding him.