Photo by Millie Pilkington/Kensington Palace via Getty Images

It has always been standard practice for two direct heirs to the throne to travel separately. 

Although, legally, this is not official royal protocol, it is standard royal practice as a failsafe. Put in place in case of any unfortunate, fatal accidents or incidents that would eliminate the Royal Family lineage en route to their destination, leaving the Royal Family in an unstable position.

According to Graham Laurie, speaking on his podcast ‘A Right Royal Podcast,’ King Charles’s former pilot explained that the current monarch, King Charles III, used to fly on the same plane as his family – Diana, Princess of Wales, Prince William and Prince Harry, when his children were young and with prior written permission from his late mother, Queen Elizabeth II.

However, this changed as soon as Prince William turned 12-years-old, after which William had to fly separately, notably in the 125 aircraft from Northolt and never boarded the same flight as his father and Prince Harry again.

Despite the Royal Family having this practice in place, Prince William also broke this tradition in April 2014, when the then Duke and Duchess of Cambridge and their firstborn, nine-month-old Prince George, embarked on their first tour of Australia and New Zealand.

However, Prince William sought permission beforehand from his late grandmother, who agreed.

Despite the Prince and Princess of Wales breaking this royal rule many times, in less than two years, once Prince George turns 12, he will have to travel separately from his father and younger siblings on all future flights, without exception.