Prince George and Princess Charlotte
Prince George and Princess Charlotte have to start bowing to the Queen when they turn 5. Pictured: Prince George and Princess Charlotte arrive at Berlin Tegel Airport during an official visit to Poland and Germany on July 19, 2017 in Berlin. Getty Images/Chris Jackson

Prince George and Princess Charlotte have to practice a certain royal rule when they turn 5 years old.

Prince William and Kate Middleton's eldest child, Prince George, has just turned 5 and according to a royal expert, he already needs to follow certain palace protocols. When royal children reach this age they have to start bowing to the queen or king. Royal historian Marlene Eilers Koenig believes that the third-in-line to the throne has already started doing this.

"Certainly by age five. The only person they will be curtsy or bow to is the sovereign. A royal highness does not curtsy to another royal highness. Yes, there are articles that state this, but it is not true," Koenig told HELLO!

"Curtseying and bowing is etiquette, nothing to do with precedence. You bow or curtsy the first time you see the sovereign and then again when you leave. At Christmas at church, we saw the Cambridges and Prince Harry and Meghan curtsy and bow when the Queen arrived and left. Other royals including Charles did not because they had come from Sandringham and had already seen the Queen," the Royal Musings blogger added.

Aside from the said protocol, Prince George has to follow a number of royal rules when he turns older. For instance, at the time, the 5-year-old royal has been seen wearing shorts. However, he has to ditch this when he turns 8 and start wearing pants.

According to the rite of passage dating back to the 16th century, young boys would only graduate to long trousers when they are 8 to signify growing up. The Duke and Duchess of Cambridge's son was only seen wearing pants once at Prince Harry and Meghan Markle's royal wedding.

Prince George can also board the same plane with his parents when he turns 12 years old. No two direct heirs are allowed to board on the same flight to prevent the line of succession from being affected in case of a crash.

Prince William and Middleton have to follow this. However, the Duke and Duchess of Sussex may not as they are down the line of succession.

In related news, Prince George has reportedly lost interest in playing with his little sister, Princess Charlotte. According to an insider, the little prince has become very independent and wants to do things on his own.