While Elizabeth's actual birthday is on April 21, she publicly celebrates her big day several weeks afterward during Trooping the Colour, which takes place on a Saturday in June when the weather is expected to be good. This has been the case for every monarch since 1748, when the Trooping the Colour ceremony was deemed the official public birthday celebration for the British sovereign.
The event is carried out by troops from the Household Division (Foot Guards and Household Cavalry) on Horse Guards Parade in Whitehall, and typically the entire royal family is present at the event to either participate in the march or to watch. Senior members of the royal family arrive to the event in carriages, and much is made of who is sitting with whom as they travel together in small groups. However, Prince Charles, Prince Edward, Princess Anne, and Prince William all ride in the event on horseback as they are members of the Royal Colonels. The Queen also rode on horseback during the event, but stopped in 1986. Likewise, Prince Philip also rode in the parade, but stopped in 2003. After the march, the royals all return to Buckingham Palace where they greet a massive crowd from their famous balcony and watch a flyover.