King Charles III and his eldest son Prince William are forbidden from flying on the same plane together.
It's a luxury most of us take for granted - hopping on a plane with your mum and dad or kids to go on holidays to faraway lands.
But for the royals, this is another thing they have to carefully think about before boarding.
Royal tradition states that Prince Charles and Prince William should never get on the same plane together, and for quite a sad reason.
Should the plane crash the monarchy would lose its current king and the heir to the throne.
The unofficial rule also applies to Prince William and his five-year-old son, Prince George, who is second in line to the throne.
Prior to the Queen's death William has flown with his whole family on many occasions, including on royal trips to Canada, Germany and Poland.
It remains to be seen whether he will continue to do so now that Prince George is second in line to the throne.
It's thought the tradition dates back to the early days of air travel, when flights weren't deemed as safe.
In the years running up to her death the Queen relaxed the rule.
A royal spokesman said in 2014: "While there is no official rule on this, it is something that the Queen has the final say on."
Prince William is now first in line to the throne and his children, George, Charlotte and Louis, are second, fourth and fifth.
While Prince Harry is only fifth in line to the throne, tradition dictates that he is not to fly with William.
If something were to happen to Charles and William prior to George turning 18, Harry would be required to serve as king until the young prince turned 18 and came of age.
In recent years the royals plane usage has come under increased scrutiny, as concern about the climate and the emissions heavy nature of air travel becomes greater.
William and Kate have been known to skip private jet usage in favour of commercial airlines.
In 2016 the Duchess of Cambridge boarded a British Airways plane for a flight to Rotterdam on an official trip, while William was spotted on a Ryanair flight to Glasgow the year before.
Prince Harry and his wife Meghan have evoked the ire of some environmentalists for regularly using a private jet despite their words of concern about the climate crisis.
