LONDON (AFP) - Prince William and his new wife Catherine took part in the pomp and pageantry as Queen Elizabeth II celebrated her official birthday on Saturday. William, her grandson, wore his wedding uniform only this time complete with a bearskin hat for the traditional Trooping the Colour military parade in central London. Dressed in the scarlet tunic of the honorary colonel of the Irish Guards, the Duke of Cambridge rode on horseback as Catherine joined other royals watching from a balcony. It was the publics first chance to see the royal family all together since William and Kates wedding on April 29, watched by an estimated two billion people around the world. The event, celebrating the queens 85th birthday, took place the day after her husband Prince Philip turned 90. He is the longest-serving consort in British history.