Kate Middleton and Prince William's eldest son Prince George, second-in-line to the throne, delights fans with his cheeky antics while out and about.

Prince George reportedly gave his classmates a stern warning about who they'd be messing with if they tried to give him any grief in the schoolyard.

Prince George, who turns 11 on July 22, is going viral on TikTok for allegedly telling his school friends "you better not mess with me" because Prince William will be a king.

Royal author Katie Nicholl revealed the young royal's playground taunt in her 2022 book The New Royals: "George understands he will one day be king and as a little boy, sparred with friends at school, outdoing his peers with the killer line: 'My dad will be king so you better watch out'."

Russell Myers was asked about the passage during an appearance on Australia's Today show, and a clip of his response has gone viral.

"This is actually hilarious because apparently in a new book, Prince George has been telling his classmates, 'Listen, you better not mess with me or my dad because he's going to be the king,'" Myers said.

"I mean it is literally the best thought of 'my dad is bigger than your dad,' isn't it? So, little cheeky George, maybe he's got a bit of his uncle Prince Harry's fighting spirit in him."

The clip was liked around 12,000 times and viewed over 108,000 times after it was posted alongside pictures of the young royal.

According to Nicholl, Prince and Princess of Wales are "raising their children, particularly Prince George, with an awareness of who he is and the role he will inherit, but they are keen not to weigh them down with a sense of duty."

Prince George was all excited when he met Taylor Swift with his father King Charles and sister Princess Charlotte during the pop superstar's London leg of Eras Tour on June 21, celebrating his father's 42nd birthday with a sweet selfie with the megastar.