Queen Elizabeth Rules! Kate Middleton and Prince William's Daughter Will Be a Princess (If They Have One!)

Kate Middleton and Prince William's first child just may be a little princess.

On what also happens to be the expectant mum's 31st birthday, Queen Elizabeth II decreed that her next great-grandchild's title will be prince or princess and be referred to as His or Her Royal Highness.

The legal decision—called a Letters Patent—overturns a 1917 decree issued by the queen's grandfather, King George V, that the Prince of Wales' eldest son would be prince but a firstborn daughter (or any daughter) wouldn't be a princess.