There’s nothing staunch monarchists love more than a good photo of the Duke and Duchess of Cambridge disembarking from their private plane with their two children, Prince George and Princess Charlotte, in tow.
Just take these recent snaps from their Poland tour:
But it turns out Prince William is breaking time-old royal protocol every time he flies with his children. Two heirs to the throne are never meant to travel on the same plane, in case, to put it bluntly, it crashes and they both die. When Prince travels with both his children, that’s three heirs to the throne on the one flight.
According to marie claire US, Prince William first sought special permission from the Queen to travel with his new son in 2014, before the family embarked on their royal tour of Australia and New Zealand.
“While there is no official rule on this, and royal heirs have traveled together in the past, it is something that the Queen has final say on,” a royal spokesperson told the BBC.
Prince William has continued to break the unwritten rule since his 2014 tour.
This article originally appeared on marie claire.