When the young prince turns 12 in 2025, he will likely be required to follow a royal travel rule that has been in place for decades, according to The Mirror. The custom secures the future of the monarchy by restricting who can travel together on the same plane—and once an heir to the throne turns 12, he or she must fly separately from all the other heirs. Prince William, as well as his father King Charles III, had to adhere to the same protocol.

Former royal pilot Graham Laurie spoke to A Right Royal Podcast about the change once Prince William turned 12 in 1994. “Interestingly, we flew all four: the Prince, the Princess, Prince William and Prince Harry, up until Prince William was 12 years old. After that, he had to have a separate aircraft and we could only fly all four together when they were young with the written permission of Her Majesty,” he explained. “When William became 12, he would fly normally in a 125 from Northolt and we would fly the 146 out with the other three on.”

The rule preserves the royal family’s future in the event of an accident, but can be eschewed with the current monarch’s permission. And while neither William nor Kate have shared whether or not they’ll follow the protocol with George, it’s unclear if it’ll be the young prince who flies solo. There’s a chance he could continue to travel with his mother and siblings while William flies on a different aircraft.

This isn’t the only morbid rule royals have to follow: They’re also required to travel with a black outfit in case someone in the family were to pass away while they’re abroad. That exact scenario played out in 1952, when Queen Elizabeth’s father King George died while she was in Kenya on a royal tour. Upon returning to the U.K., a black dress was brought onboard to her for a quick change before she disembarked the plane.

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