Under protocols established by George V in letters patent more than 100 years ago in 1917, the children and grandchildren of a sovereign have the automatic right to the title HRH and prince or princess.
At the time Archie was born, he was the great-grandchild of a sovereign, not a grandchild.
George V’s declaration sets out: “The grandchildren of the sons of any such sovereign in the direct male line (save only the eldest living son of the eldest son of the Prince of Wales) shall have and enjoy in all occasions the style and title enjoyed by the children of dukes of this realm.”
As such, Archie will be entitled to the titles when Prince Charles accedes the throne.
George V’s declaration means that only Prince George, as a great-grandson of the monarch down the direct line of succession to the throne, was originally entitled to be a prince, as he is the eldest son of the eldest son of the Prince of Wales.
The Queen did step in ahead of George’s birth to issue letters patent to ensure the Duke and Duchess of Cambridge’s children would have the titles of prince and princess.
But they are children of the future monarch, whereas Archie is not. His father, Harry, is sixth in line to the throne, and will move down the line of succession if William and Kate have more children, and as George, Charlotte and Louis have children of their own.