Prince Harry is expected to speak at Saturday evening’s event, in his new role as president of The Queen’s Commonwealth Trust.
Special gun salutes are also being staged midday Saturday in central London to mark the occasion.
The queen celebrates two birthdays every year: Her actual birthday on Apr. 21, which she usually marks privately with her family, and her “official birthday” in the summer. That usually falls on the second Saturday in June, when she joins the Trooping the Color military parade in central London.
Meanwhile, Prince Charles, the 69-year-old heir to the British throne, has been approved as the next head of the 53-nation Commonwealth of the U.K. and its former colonies. British Prime Minister Theresa May said the decision was unanimous, but it had not been a foregone conclusion.
Elizabeth has led the Commonwealth since she became queen in 1952. However, the position is not hereditary, and some people have suggested a non-royal leader would give the group a more modern profile. Elizabeth has said it was her “sincere wish” that Prince Charles would follow her in the role, the BBC reports.
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