Prince William has revealed that sometimes it's not easy to travel with his kids.

The Duke and Duchess of Cambridge often travel abroad as part of their royal duties. Sometimes, their trips would take a couple of days or weeks, which means that they would have to be away from their children for a while. As such, there are times when Prince William and Kate Middleton bring them along.

In fact, in 2016, Prince William and Middleton visited Canada with Prince George and Princess Charlotte. However, the royal tour wasn't easy with kids traveling with them, especially since Prince George was only 3 years old and Princess Charlotte 17 months old at that time.

"The jet lag has been a bit interesting since we got back," Prince William said on how his kids adjusted to their trip (via Express).

He also praised the two for being in their "best behavior," adding that it was "nice to take the children with us."

Prince William and Middleton didn't take Prince George and Princess Charlotte when they visited India during the same year. The duchess revealed that they opted to leave their son home because he was "naughty."

"Because George is too naughty," Middleton said. "He would be running all over the place. The next time we come we will definitely bring them."

The Duke and Duchess of Cambridge are reportedly not allowed to travel with their firstborn. The royals have an unwritten protocol that prohibits the heirs from flying in the same plane.

This aims to prevent the line of succession from being affected in case of a crash. Prince William is the second in line to the throne, while Prince George is third in the succession.

However, Prince William and Middleton were able to travel with Prince George after the duke asked the Queen's permission. The travel rule was not official and "it is something that the Queen has the final say on."

Prince William and Middleton are expected to continue to break this travel rule with Prince Louis. The Duke and Duchess of Cambridge have already brought Prince George and Princess Charlotte in some of their trips abroad, the couple is expected to do the same with Prince Louis.

Prince William, Kate Middleton, Prince George and Princess Charlotte
Prince William reveals that hardest part when traveling with Prince George and Princess Charlotte. Pictured: Prince William, Prince George, Kate Middleton and Princess Charlotte on the tarmac of the Airbus compound in Hamburg, northern Germany, on July 21,2017. Getty Images/Patrik Stollarz