The Prince and Princess of Wales broke the rules around royal travel when their eldest children, Prince George and Princess Charlotte, joined them on their overseas tours.
It's long been an unwritten rule that two heirs shouldn't travel on the same flight but Prince William and Prince George travelled together to Australia in 2014, Canada in 2016 and Germany and Poland in 2017.
William reportedly asked permission from the late Queen for George to accompany him and Kate on their visit to Australia and New Zealand.
But the rules could be about to change for 11-year-old George in the next year, and he may no longer travel with his parents and younger siblings, Princess Charlotte, nine, and Prince Louis, six.
Former royal pilot Graham Laurie confirmed on an episode of HELLO!'s A Right Royal Podcast last year when William turned 12, he began travelling in a different aircraft to his family.
© GettySpeaking about transporting Charles, Diana, William and Harry on family trips, Graham recalled: "The ones I did [holiday flights] mainly were the ones when the Wales' went to the Mediterranean.
"But interestingly, we flew all four: the Prince, the Princess, Prince William and Prince Harry, up until when 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.
"Nowadays, for instance, the King can't fly with the Prince of Wales."
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Graham continued: "So, what we did in the end, when William became 12, he would fly normally in a 125 from Northolt and we would fly the 146 or the Andover out with the other three on.
Explaining the decision for the change when William turned 12: "Up until then, they probably thought it will be too much for him travelling on his own. But nevertheless, that's what they did."
© Getty ImagesWhen asked if this rule would apply to today's royals, with Prince William and Prince George, Graham said: "I know the King is trying to cut down cost and is aware of travel, but I think the safety side is still paramount."
Other significant changes have been made to royal travel, particularly when it comes to security.
Graham explains: "Our aircraft were painted red, white and blue… but they changed the colour scheme in 2002 to look more like a normal airliner."
