Prince George turned 12 today with the major milestone set to bring about big changes for the future king.

Royal protocol dictates the young prince will not be allowed to fly on the same aircraft as his father, Prince William, without permission from King Charles III.

George is the eldest child of Prince William, who is heir to the throne, and Princess Catherine.

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Traditionally, direct heirs to the British throne have not been able to travel together in case of an emergency or an accident that could wipe out the entire royal line.

William and Catherine have two more children, Princess Charlotte, 10, and Prince Louis, 7, but the rule only applies to the first two direct heirs to the throne — William and George.

The Prince of Wales was the same age when he stopped flying alongside his father, then the Prince of Wales and now King Charles, to protect the monarchy’s line of succession.

King Charles’ former pilot Graham Laurie said he initially flew Charles, Diana, William and Harry all together but that changed once William turned 12.

“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 told Right Royal Podcast.

If the Prince and Princess did want to fly with all three children they would have to request permission from King Charles.

Speaking on Sunrise on Tuesday, Royal editor Rob Jobson revealed George had previously flown in a helicopter with his dad and the rest of the family.

“But the late Queen and Charles confronted William about it,” Jobson added.

“That is probably going to have to stop.”

It is uncertain what William and Catherine will do, but they have always worked to give their children a normal upbringing while still preparing them as best as possible for their future royal roles.

While George is still too young to attend official royal briefings, he is being mentored by his father.

“I think he has had a lot of experience that others didn’t have.,” Jobson said.

“He was at the coronation as a page boy to his grandfather. He has seen the sadness of the state funeral of Queen Elizabeth, his great-grandmother.

“All of these things he has been witness to.”