Diana 's full title , while married , was Her Royal Highness The Princess Charles Philip Arthur George , Princess of Wales and Countess of Chester , Duchess of Cornwall , Duchess of Rothesay , Countess of Carrick , Baroness of Renfrew , Lady of the Isles , Princess of Scotland . Diana 's full title , while married , was Her Royal Highness The Princess Charles Philip Arthur George , Princess of Wales & Countess of Chester , Duchess of Cornwall , Duchess of Rothesay , Countess of Carrick , Baroness of Renfrew , Lady of the Isles , Princess of Scotland .