Why William won't have to follow this travel rule when he becomes King - but Kate will

The royals have their own unique set of rules and traditions when flying. Did you know that the Princess of Wales Kate Middleton's dresses get their own seats on a plane? Or that the late Queen Elizabeth II always carried very specific teabags with her when she travelled? And there's also the little known fact that the senior royals reportedly carry bags of their own blood type.

Prince William and Kate Middleton are also known to break the royal rules when going abroad. The couple often fly with their three children, Prince George, Princess Charlotte and Prince Louis, which is against royal protocol as two heirs must not travel together in order to protect the royal lineage.

However, when William becomes King there will be one major difference in the way he travels compared to his wife - and there's a rule that cannot be broken.

Currently, when the the Wales' go overseas they must adhere to passport checks and go through immigration. But when William takes the throne, he will no longer have to do this. Instead, the rules that now apply to the monarch will apply to him.

As the King, Charles is the only person in the UK permitted to travel without a passport, and therefore William will not need one to board a flight when he takes on the role.

However, Kate will still have to carry the travel document with her despite becoming the Queen Consort. This is because passports are issued in the name of the monarch.

It states: "His Britannic Majesty's Secretary of State requests and requires in the name of His Majesty all those whom it may concern to allow the bearer to pass freely without let or hindrance and to afford the bearer such assistance and protection as may be necessary."

Prince William is next in line to travel passport-free, followed by his eldest son, George.

Despite this, the King does still need to answer questions, such as his age and address, for security reasons.