Britain's Duke and Duchess of Cambridge's baby will be a princess if it is a girl.

Prince William and Duchess Catherine are expecting their first child together and the duke's grandmother Queen Elizabeth has declared that if the couple have a daughter, she will be granted the title of princess.

A notice published in Wednesday's (09.01.13) London Gazette announced the decision, reading: ''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 past rules only a first-born boy born to William and Catherine - who was known as Kate Middleton before her wedding in April 2011 - would automatically become a prince, while a daughter would have been called Lady.

Also, if Kate - who is believed to be just over 12 weeks pregnant - has twin boys or a second son at a later date, any second born son would be treated as the son of a Duke and would not be an HRH, but instead would have the title Lord.