Queen Elizabeth, Prince Philip, Lady Louise Windsor and Catherine, Duchess of Cambridge stand on the Buckingham Palace balcony following the Queen’s Birthday Parade, ‘Trooping the Colour’ at Horse Guards Parade in London yesterday. The ceremony is believed to have first been performed during the reign of King Charles II. In 1748, it was decided that the parade would be used to mark the official birthday of the sovereign. More than 600 guardsmen and cavalry make up the parade, a celebration of the sovereign’s official birthday, although the Queen’s actual birthday is on April 21.