The Royal Windsor Horse Show has been:
…an annual fixture for which the Royal Family have a great affection.
Held annually for five days in May or June in Windsor Home Park, the Royal Windsor Horse Show has always enjoyed the enthusiastic support of the Royal Family.
It began in 1943 with the founding of the Royal Windsor Horse Show Club which was set up to hold horse shows for charity. King George VI became its Patron and the first Royal Windsor Horse was held on 27 May 1944, attended by numerous members of the Royal Family including the King and Queen. Princess Elizabeth (now our current Queen) won the Single Private Driving on her pony Hans and Princess Margaret won the Wartime Utility Driving Class on the King’s Fell pony Gipsy.
The show steadily grew in popularity and size during the latter half of the 20th century and Royal involvement continued. The Queen became Patron in 1952, and two years later she donated The Queen’s Cup for Armed Services team jumping.
Her Majesty still attends each year along with other members of her family.(source)
With that being said, here is yet another documentary about the Royal Windsor Horse show with appearance and commentary from The Duke of Edinburgh.
Photo courtesy of: Royal.gov.uk