If the Duke and Duchess of Cambridge have a baby girl she will be titled 'Princess', according to a report in the London Daily Mirror, 9 January, 2012.
Under past rules, a girl born to William and Kate would have been styled 'Lady' and not known as 'Her Royal Highness' – only a first-born boy would automatically become a Prince.
But ahead of the proposed changes to royal succession, The Queen has taken action by new Letters Patent to ensure that her future great-granddaughter title would have a title suitable for a future monarch.
The announcement came as the Duchess of Cambridge celebrated her 31st birthday today.
A notice published in the London Gazette of 8 January, 2013 stated:
"The Queen has been pleased by Letters Patent under the Great Seal of the Realm dated 31 December 2012 to declare that all the children of the eldest son of the Prince of Wales should have and enjoy the style, title and attribute of royal highness with the titular dignity of Prince or Princess prefixed to their Christian names or with such other titles of honour."
Under Letters Patent issued by William's great great grandfather King George V in 1917, had limited titles within the Royal Family.
It declared that "the children of any Sovereign of these Realms and the children of the sons of any such Sovereign and the eldest living son of the eldest son of the Prince of Wales shall have and at all times hold and enjoy the style title or attribute of Royal Highness with their titular dignity of Prince or Princess".