Why Kate Middleton Can’t Always Travel With Prince William, Prince George

She may be the mother of the current members of the royal family who are third, fourth and fifth in line for the throne, but a specific piece of royal protocol means that Kate Middleton won’t be able to travel with her children—or even her husband—once they reach a certain age.

According to Express UK, an old rule that dates back to the early days of air travel states that Monarchs and their heirs are not allowed to travel together on planes in case of a tragic accident. The rule prevents the entire royal lineage from being wiped out in that extreme case. This would also mean that Middleton cannot travel with her husband, Prince William, or eldest child, Prince George, specifically.

However, the rule has undergone some relaxation in recent years by the Queen, who has permitted the Duchess of Cambridge to still travel with the rest of her family. This is only going to be allowed however until Prince George turns 12. Upon that day, he and Prince William will be required to fly separately. Though Middleton is not strictly governed from traveling with either, she won’t be allowed to travel with both at once.

The same tradition has meant that Prince Charles and Prince William are also not allowed to board the same flight together either, and the rule is applied in both cases of private planes and commercial flights.

However, for now, the Duke and Duchess of Cambridge will likely continue traveling with all of their children together on the same flight, as Prince George will be turning six-years-old next month. By comparison, his siblings, Princess Charlotte and Prince Louis, are four-years-old and one-years-old respectively.