The Daily Mirror reveals that in Katie Nicholl's new book The New Royals, George has previously told his classmates, "My dad will be king so you better watch out," when they were teasing him.
Katie writes, "They 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.
"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.'"
George, along with his siblings, Princess Charlotte, seven, and Prince Louis, four, recently started at the elite Lambrook School in Berkshire, west London. George and Charlotte previously attended Thomas' Battersea.
It comes after George and Charlotte attended the Queen's funeral last week, while Louis was deemed too young.
However, Kate Middleton revealed Louis' devastating words following Her Majesty's passing, telling Australia's Governor-General David Hurley at Buckingham Palace earlier this month that while George was "now realising how important his great-grandmother was", Louis was asking questions about "playing games".
"The younger one is sort of asking questions like, 'Oh does that mean we can still play these games when we go to Balmoral and things like that, cause she's not going to be there?'" Hurley said.
Kate previously told mourners during a walkabout in Windsor that Louis said, "At least grannie is with great-grandpa now".
Never miss a thing. Sign up to Yahoo Lifestyle’s daily newsletter.
Or if you have a story idea, email us at firstname.lastname@example.org.