In around six months, Kate Middleton will have to pick between their children whenever they board a helicopter or aeroplane flight as the British Royal Family introduces a new rule banning immediate heirs to the throne from flying in the same vehicle.

The introduction of the clause aims to ensure that should the worst situation happen and an aircraft crashes, there will still be a successor to the throne to prevent a disastrous situation for the future of the United Kingdom’s monarchy.

That means when Prince George, who is second in the line of succession, turns 12 on July 22, he and Princess Charlotte will not be allowed to fly together. The rule also applies to his father, Prince William, who will ascend the throne upon the eventual death of King Charles III.

Until July 22, the family have been allowed to fly together. George will likely accompany his mother on flights since she cannot inherit the throne, whilst Prince William, Princess Charlotte and Prince Louis could all potentially ascend should something tragic happen to those before them.

After Prince William and his three children, Prince Harry is next in the line of succession and is followed by his two children with Meghan Markle. However, it’s unlikely that he will ever inherit the throne. The last time a brother ascended to the throne in the place of their older sibling was with Prince George VI in 1936.

Named Albert Frederick Arthur George, he was the younger brother of Prince (and briefly king) Edward VIII. Edward walked away from the throne in December after just nine months in order to begin a relationship with Wallis Simpson.

Simpson was an American two-time divorcee, and marrying a divorced person was heavily frowned upon in the 1930s. Edward was not permitted by the Church of England to marry her, so he gave up his status as king instead.

They married in 1937 and remained married until Edward died in 1972. Simpson remained widowed until her death in 1989. The pair are buried together close to Windsor Castle.