Britain's Queen Elizabeth II "died peacefully" on Thursday, according to a statement from Buckingham Palace. She was 96.

The news of her death came just hours after the palace announced that the queen's doctors were "concerned" about her health and were keeping her under "medical supervision" at Balmoral Castle, the British royal family's estate in Aberdeenshire, Scotland, where she has been vacationing this summer.

Members of the royal family, including the queen's four children, quickly gathered by her side at Balmoral, according to their respective spokespersons. She died that afternoon.

Elizabeth was Britain's longest-reigning monarch. She ascended to the throne in 1952 and, in June, celebrated her Platinum Jubilee, marking 70 years as queen. Her eldest son, Charles, Prince of Wales, will take his mother's place on the British throne as king. Charles' wife, Camilla, Duchess of Cornwall, will become known as queen consort.

Source: AbcNews