As is tradition, Prince William and Kate Middleton’s royal rules must be followed at every step—and that even includes when they’re on vacation. But this time around, it looks like the Cambridges decided to do things a little bit differently.

Prince William, 39, and Duchess Kate, 39, were recently spotted at London’s Heathrow airport on Thursday, October 21 with their three children: Prince George, 8, Princess Charlotte, 6, and Prince Louis, 3. The family of five are taking advantage of the half term (the fall school break, for our non-UK readers) and headed on their first holiday abroad in over a year together.

While it’s unclear where, exactly, the Cambridges are headed, some speculate that the family could be visiting Greece for the wedding of the late Princess Diana’s godson, Prince Philippos, and his bride, Nina Flohr. Wherever they’re going, it’s clear that the royals will be gone for some time as they decided to bring along their trusted nanny, Maria Teresa Turrion Borrallo, to watch after their children during the trip.

Of course, the Cambridge family’s recent sighting at the airport also made headlines for more reasons than their vacation alone. It turns out that the Duke and Duchess broke a royal rule by traveling with their children in tow. There is a longstanding protocol within the royal family that would typically prevent royal family members from traveling in the same car or plane together. This rule exists as a way to protect future heirs to the throne in the event of fatal accidents.

So, how were Prince William and Duchess Kate able to bend the rules this time around? According to Express, Queen Elizabeth can grant special permission for royal families to travel together as long as they get her approval first. However, in a few years time, there will be no further exceptions to the rule. According to the site, Prince George will have to start traveling in a different plane or vehicle than his father, Prince William one he turns 12 years old. The young prince is third in line to the throne behind his dad, meaning he must be protected at all costs—even if that means flying solo.