Prince William is breaking royal protocol by flying with his kids

The best part about a royal tour? Well, obviously any Prince George or Princess Charlotte sightings.

Through the years, George and Charlotte's most adorable moments happen when they disembark planes with their mom and dad. We still can't get over Charlotte's first attempt at a curtsy, or George's priceless post-flight face.

Unbeknownst to most, Prince William has actually been breaking unofficial royal protocol by flying with his children.

William's father, Prince Charles, is the current heir to the throne followed by William and his kids, Prince George and Princess Charlotte. It has been standard practice, thought not official, for those in the succession to the throne to travel separately so that if anything should happen to the plane, their royal lineage would stay intact. In fact, George and Charlotte shouldn't be traveling on the same plane either.

A spokesperson for the royal family told the BBC at the time, "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."

Prince William asked the Queen for permission to travel with Prince George on their royal tour to Australia and New Zealand in 2014 when his son was less than a year old. Most recently, Kate and William brought their kiddos along to Poland and Germany. And if you recall, George and Charlotte also accompanied their parents to Canada last year.

Breaking protocol is nothing new for the royal couple. When it comes to raising their children, Kate is reportedly "keeping stuffy ­royal protocol far from their apartment at Kensington Palace."

Check out the slideshow above for Prince George's cutest royal tour moments!