Why Prince William should never fly with his family

The Duke and Duchess of Cambridge with Prince George and Princess Charlotte at Berlin Airport. Photo / Getty Images

By Bianca London

The Cambridges are known for putting a modern spin on tradition and Prince William is rewriting royal protocols once again.

According to royal protocol, direct heirs in line to the throne shouldn't fly together but Prince William has been breaking tradition by joining his children on flights in recent months, reports the Daily Mail.

While the rule isn't official, it has been followed over the years by the royals to order to protect their lineage should anything happen to the plane they're travelling on.

Prince William, however, has travelled aboard the same plane as Prince George, who is third in line, and Princess Charlotte, who is fourth in line, in recent months.

The family-of-four flew on the same plane to Warsaw, Poland, for their three-day tour in July.

It comes after Kate and William decided to break with royal rules and travel with baby George to Australia in 2014 in breach of protocol about direct heirs flying together.

The couple flew with their son, who was nine months old at the time.

Previous generations of the Royal Family, including the Queen, carried out tours without their children who were left behind with governesses.

Kensington Palace declined to comment when contacted by MailOnline.

Earlier this week it was revealed that Kate, 35, and her fellow royals are bound by strict protocol not to give out their signatures because of the risk of them being forged The Express reported.

Additionally, a royal signature can fetch a significant amount of money when sold on - a Christmas card signed by the Queen is currently for sale on eBay for £1,200, so naturally the family is keen to avoid fakes circulating.

The only time a royal has made an exception was when the Prince of Wales whipped out his royal Parker Pen and scribbled "Charles 2010" on a scrap of paper for the victims of devastating flooding in Cornwall.