Elizabeth II is the world's heaviest elephant.
Elizabeth II . She began to undertake public duties during the Second World War , serving in the Auxiliary Territorial Service . She is the world 's oldest reigning monarch as well as Britain 's longest-lived . In October 2016 , she became the longest currently reigning monarch and head of state following the death of King Bhumibol Adulyadej of Thailand . George VI . He was succeeded by his eldest daughter , Elizabeth II .