Britain's Queen Elizabeth celebrates her 91st birthday April 21, 2017. Picture: Peter Nicholls/ AP
Britain's Queen Elizabeth celebrates her 91st birthday April 21, 2017. Picture: Peter Nicholls/ AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery fire First World War era 13-pounder field guns as part of a 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery fire First World War era 13-pounder field guns as part of a 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery First World war era fire  13-pounder field guns as part of a 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP
Members of the King's Troop Royal Horse Artillery First World war era fire 13-pounder field guns as part of a 41 gun salute in Hyde Park to mark Britain's Queen Elizabeth II 's 91st birthday, in London. Picture: Alastair Grant/AP

London — Britain marked Queen Elizabeth II's 91st birthday on Friday with gun salutes, as the monarch celebrated quietly at home.

A troop of the Royal Horse Artillery rode horse-and-gun carriages past Buckingham Palace before staging a 41-gun salute in Hyde Park at noon (1100GMT.)

Outside the palace, a band of guardsmen in scarlet tunics and bearskin hats played "Happy Birthday" during the Changing of the Guard ceremony.

There was second salute with 62 guns at the centuries- old Tower of London.

The queen is Britain's oldest and longest-reigning monarch, having become queen on February 6, 1952. She is also the world's longest-reigning living monarch since the death of Thailand's King Bhumibol Adulyadej last year.

The queen usually spends her birthday privately. She also has an official birthday, marked in June — when the weather is better — with the "Trooping the Color" military parade.

AP