Queen Elizabeth live updates: Royal family gathers by her side at Balmoral Castle

Buckingham Palace said the queen remains "under medical supervision."

Britain's Queen Elizabeth II remains under "medical supervision," Buckingham Palace said Thursday.

According to the palace, the queen's doctors are "concerned" about her health and are monitoring her at Balmoral Castle, the British royal family's estate in Aberdeenshire, Scotland, where she has been vacationing this summer.

At age 96, Elizabeth is Britain's longest-reigning monarch. She ascended to the throne in 1952 and, in June, celebrated her Platinum Jubilee, marking 70 years as queen.

Members of the British royal family, including the queen's four children, are now gathering by her side at Balmoral, according to their respective spokespersons.