Sharp-eyed tourists outside Buckingham Palace had a rare opportunity to see Prince William on horseback.

William was taking part Saturday in rehearsals for next week's "Trooping the Colour" ceremony to mark Queen Elizabeth II's official birthday.

The 28-year-old prince and hundreds of other soldiers practiced on a hot sunny day. He was wearing a red tunic with a blue sash from the Irish Guards as he rode a mottled gray horse called Wellesley.

The queen turned 85 in April, but tradition holds that "Trooping the Colour" — the public party for the monarch's birthday — is held in June when the weather is better. The custom dates from 1748.

William and his new wife Kate Middleton plan to visit Canada and California in late June and early July.