Prince George has an official title which he only bears because his great-grandmother the Queen decided to step in and change the rules. Thanks to her, he is now officially known as His Royal Highness Prince George of Wales (Previously Prince George of Cambridge). His full name is George Alexander Louis, with Louis in honour of King Charles III's mentor Lord Louis Mountbatten, who died in an IRA bombing in 1979 - his brother's namesake.
Prince George was given the HRH title after the Queen intervened to overwrite a rule put in place by King George V, the Express reported. In 1917, he set out new guidance on which royals were allowed to have titles - and who was too far down the line of succession to qualify for one.
For the latest updates as the world mourns the Queen and King Charles III's reign begins, follow our live blog.
He had previously decided that all of the sovereign's children would automatically become a Prince or Princess, as well as any grandchildren who were born through the male line, but great-grandchildren were not included in the list.
This caused a bit of an issue when Prince George was born, as despite being our future king he wouldn't have technically had the title.
To change things, the Queen decided that George would get a title despite the rule, and decided to extend the change to all of Kate and William's children.
This means Charlotte and Louis, who are further down the line of succession and are unlikely to ever sit on the throne, are also a prince and princesses.
If the late monarch hadn't made the change, they would have likely been called Master or Lady.
The Queen didn't make this same change for Prince Harry and Meghan Markle's son, which caused rows following their interview with Oprah Winfrey.
However, Archie and Lilibet Mountbatten-Windsor are now entitled to HRH titles as they are the grandchildren of the King.
You can leave your tributes to Queen Elizabeth II here
