(LONDON) — Britain’s Queen Elizabeth II is under “medical supervision” on Thursday, according to Buckingham Palace.

The queen is being monitored by doctors at Balmoral Castle, the royal family’s estate in Aberdeenshire, Scotland.

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 on the throne.

The queen’s royal family members, including her four children, are now gathering by her side in Balmoral, according to the palace.

Here’s how the news is developing. All times Eastern:

Sep 08, 10:05 AM EDT
UK prime minister ‘deeply concerned’ about queen

U.K. Prime Minister Liz Truss took to Twitter on Thursday to say that her “thoughts — and the thoughts of people across our United Kingdom — are with Her Majesty The Queen and her family at this time.”

“The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime,” Truss tweeted.

Truss, who was recently selected as the new leader of the United Kingdom’s ruling Conservative Party, had an audience with the queen at Balmoral Castle in Scotland on Tuesday, during which she was formally asked to form a new government as prime minister after Boris Johnson’s official resignation. It was the first time in the queen’s 70-year reign that the ceremonial transfer of power was held at Balmoral, rather than at Buckingham Palace in London.

Sep 08, 9:41 AM EDT
Senior royals head to Balmoral Castle

Senior members of the British royal family are either at or on their way to Balmoral Castle in Scotland, where Queen Elizabeth II remains “under medical supervision.”

The queen’s oldest child and the heir to her throne, Charles, prince of Wales; and his wife, Camilla, duchess of Cornwall; as well as the queen’s daughter, Princess Anne, are already at Balmoral, according to their respective spokespersons.

Meanwhile, the queen’s other sons, Prince Andrew, duke of York; and Prince Edward, earl of Wessex; as well as Edward’s wife, Sophie, countess of Wessex; Charles’ two sons, Prince William, duke of Cambridge; Prince Harry, duke of Sussex; and Harry’s wife, Meghan, duchess of Sussex, are all on their way to Balmoral, their respective spokespersons confirmed.

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