When Prince Louis was born in 2018 he was automatically bestowed with an HRH title, as his older siblings Prince George and Princess Charlotte had been.

The youngster’s official full title is His Royal Highness Prince Louis of Wales, quite impressive given he has only just celebrated his sixth birthday.

However he only received his royal title thanks to his late great-grandmother Queen Elizabeth implementing a change to one rule that had been in place since 1917.

Over one hundred years ago the then-monarch, King George V, set out guidance explaining which members of the Royal Family would qualify for a title and which would not.

He made the decision that all of the sovereign’s children would automatically be a Prince or Princess, as well as any grandchildren born through the male line.

Prince Louis nearly missed out on a royal title (Image: Getty)

But his rule did not apply to any of the monarch’s great-granchildren, which would have included George, Charlotte and Louis when they were born.

Ahead of George’s birth in July 2013 the late Queen decided to amend the rule so that the future King would be born with a royal title.

This change was then extended to Charlotte and Louis when they arrived in May 2015 and April 2018 respectively, and will likely apply to the future great-grandchildren of any monarch.

Queen Elizabeth made the change for her great-grandchildren (Image: Getty)

Even if the late Queen had not made the change, the Wales children would have inherited their titles once their grandfather Charles became King.

His Majesty and Queen Camilla will be appearing at Trooping the Colour on June 15, and while Prince William is likely to attend Princess Kate will remain away.

She has been absent from public life while she receives preventative chemotherapy, as she announced her cancer diagnosis via a touchingly personal video message in March.

The King and Queen will be at Trooping the Colour this year (Image: Getty)

Royal expert Richard Fitzwilliams told Express.co.uk the Prince of Wales is expected to be there due to his military role, but he may not bring the children with him.

Mr Fitzwilliams said: “I am sure that William will attend as Colonel of the Welsh Guards. Obviously, Catherine is unlikely to because of her health and it may well be that their children will miss this year’s Birthday Parade.”

Other non-working royals such as Princess Beatrice, Princess Eugenie, Peter Phillips and Zara and Mike Tindall may be invited onto the Buckingham Palace balcony instead to boost numbers.