Updated: September 9, 2022 8:20 AM EDT | Originally published: September 8, 2022 9:07 AM EDT

Update: Queen Elizabeth II died on Sept. 8, 2022. Read her obituary here.

Britain is on high alert following the announcement that Queen Elizabeth II was put under medical supervision at her Balmoral estate in Scotland after her doctors expressed concerns about her health.

Although the world’s longest-reigning monarch, aged 96, has scaled back her royal duties in recent years—including most recently her decision to appoint the country’s new Prime Minister Liz Truss from Balmoral instead of Buckingham Palace, where such appointments are traditionally done—the announcement on the status of her health is nonetheless a significant development.

What we know about her health

Buckingham Palace announced in a statement Thursday that “the Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision.” They noted that she “remains comfortable” at the Balmoral estate. No other details have been made public but Buckingham Palace doesn’t issue such statements lightly.

Back in February, the Queen tested positive for COVID-19 but she eventually recovered. She described the ordeal as leaving her “very tired and exhausted.” Buckingham Palace said she had been dealing with “mild cold-like symptoms.”

Queen Elizabeth II has also suffered from back pain over the years and had knee surgery in the 2000s. In October, the Queen was admitted to hospital for an overnight stay in what Buckingham Palace called “preliminary investigations.”

The Queen has been suffering from “mobility issues”—using a cane and delegating more duties to Charles.

Royal family rushes to Balmoral Castle to be with Queen

Royal family members have traveled to Balmoral to be at the Queen’s side. Spokespeople for royal family members confirmed that all of the Queen’s four children, including Prince Charles and his wife, Camilla Parker-Bowles, are currently with the Queen.

Prince William has just landed in Scotland, leaving behind Kate, Duchess of Cambridge, who is staying in Windsor to care for her children who are attending their first day of school. A spokesperson for Harry and Meghan, the Duke and Duchess of Sussex, confirmed to Buzzfeed News that Prince Harry, who was already in the U.K. for previous engagements with his wife, will also be traveling to Balmoral alone. Meghan Markle will remain in London, and will no longer attend the WellChild awards. Sources have indicated that Markle may join Harry at a later date.

The fact that senior members of the royal family, including the Queen’s immediate successors Prince Charles and Prince William, are gathering at Balmoral to be with the monarch suggests that the prognosis is serious.

The BBC, the country’s national broadcaster, has suspended its regular programming until 6 p.m. local time and its anchors are wearing black attire, in apparent preparation for the worst.

Read More: See Every TIME Cover Featuring Queen Elizabeth II

The political implications

The development comes at an already critical political juncture for Britain, which only days ago welcomed its 56th Prime Minister, Liz Truss, to Downing Street. (Truss currently has no plans to travel to Scotland.) The last public image of the Queen was released following her formal swearing in of Truss to the premiership on Tuesday, the 15th such appointment to take place during the Queen’s 70-year reign. (The first, Winston Churchill, was appointed in 1952). “The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime,” Truss said in a statement on her Twitter account. Similar outpourings of support for the Queen were issued by British leaders across the political spectrum.

What happens in the event the Queen dies?

There are meticulous procedures in place for what should happen in the event of the monarch’s passing. Dubbed “Operation London Bridge,” the news of the Queen’s death would be communicated to the Prime Minister by the Queen’s private secretary, Sir Edward Young, as well as to the cabinet secretary (the country’s most senior civil servant) and other senior ministers. Flags across Whitehall, the neighborhood where the British government sits, would be lowered to half-mast. The U.K. Parliament as well as its devolved legislatures in Northern Ireland, Scotland, and Wales would be adjourned. An “Official Notification” would be pinned to the gates of Buckingham Palace informing the public of the monarch’s death.

— With additional reporting by Sanya Mansoor and Solcyre Burga

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Write to Yasmeen Serhan at yasmeen.serhan@time.com.

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