The succession list on the royal family website was updated to reflect the change a day after Harry and Meghan first referred to their daughter Lilibet as Princess, following her christening ceremony in the US.

Prince Harry and Meghan Markle, Duke and Duchess of Sussex

The children of Prince Harry and Meghan Markle, the Duke and Duchess of Sussex, were on Thursday added to the royal titles list on the official Buckingham Palace website and will be formally known as Prince Archie and Princess Lilibet of Sussex.

The succession list on the royal family website was updated to reflect the change a day after Harry and Meghan first referred to their daughter Lilibet as Princess, following her christening ceremony in the US.

Previously, they were listed as Master Archie Mountbatten-Windsor and Miss Lilibet Mountbatten-Windsor.

As per the rules for the titles of Britain’s royalty, Archie and Lilibet were not automatically made prince and princess at birth because they were then the great-grandchildren of the monarch – the late Queen Elizabeth II. But they gained the automatic right to their titles once their grandfather, King Charles III, acceded to the British throne.

"The children's titles have been a birth right since their grandfather became monarch. This matter has been settled for some time in alignment with Buckingham Palace," a spokesperson for the Duke and Duchess of Sussex has been reported as saying.

The rules for royal titles were set out by Britain's King George V, the grandfather of Queen Elizabeth II, in 1917.

Under those norms, the Sussexes are also entitled to use the His or Her Royal Highness (HRH) prefixes but Harry and Meghan no longer use these titles after leaving frontline monarchy in 2020.

It is understood the prince and princess titles for their children – Archie, 3, and Lilibet, 21 months – will also be used only in formal settings but not in everyday conversational use.

The change follows a confirmation of Lilibet’s christening as Princess Lilibet Diana at a private ceremony at the Sussexes' home in Montecito, California.

It comes amid strained relations within Britain's royal family following a controversial tell-all Netflix documentary by the Duke and Duchess and Harry’s memoir ‘Spare’, which revealed many intimate details of his relationship with his father and brother.