The Duke and Duchess of Cambridge went on a tour of Poland and Germany with their two children in tow this summer.
This, it turns out, is highly unusual.
According to BBC, heirs to the throne do not tend to travel together. This is so that in the case of tragedy, the line of succession remains protected.
Prince William and Prince George should not be travelling together, much less should they share a plane.
A way around the archaic (though coldly logical directive) is to simply seek permission from the queen.
The royal press office told BBC’s Newsround:
While there is no official rule on this, and royal heirs have travelled together in the past, it is something that the queen has the final say on.
So why did they insist on travelling together?
We're not sure - it could be the prince simply wanted to travel with his family. After all, this isn't the first time - Prince William has previously asked permission from the queen before he took Prince George with him on a trip to New Zealand and Australia.
His reasoning may be unknown, but one thing's for sure - these adorable pictures of Prince George and Princess Charlotte are reason enough, IMO:
Duchess of Cambridge and Princess Charlotte
Prince William, Duchess of Cambridge, Prince George and Princess Charlotte