LONDON (AP) — Queen Elizabeth II, Britain’s longest-reigning monarch has died. She was 96.

Buckingham Palace made the announcement in a statement Thursday.

A link to the almost-vanished generation that fought World War II, she was the only monarch most Britons have ever known, and her name defines an age: the modern Elizabethan Era. The impact of her loss will be huge, and unpredictable, both for the nation and for the monarchy, an institution she helped stabilize and modernize across decades of huge social change and family scandals.

With the death of the queen, her son Charles, automatically becomes monarch, even though the coronation might not take place for months. It is not known whether he will choose to call himself King Charles III or some other name.

The queen was under medical supervision at her summer residence in Scotland after doctors raised concerns about the 96-year-old monarch’s health as members of the royal family rushed to be at her side.

“Following further evaluation this morning, the Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision,” a palace spokesperson said, speaking on condition of anonymity in line with customary policy. “The Queen remains comfortable and at Balmoral.”

The palace declined to provide further details about the queen’s condition, but there were worrying signs that it might be serious. A Cabinet minister interrupted Truss during a debate in the House of Commons to inform her about Elizabeth’s condition and family members canceled long-planned engagements to travel to the Highlands.

Prince Charles, the heir to the throne, along with his wife, Camilla, and sister, Princess Anne, were with the queen at Balmoral Castle, her summer residence in Scotland. Other members of the royal family, including Charles’ sons, Princes William and Harry, were said to be en route.

The gathering of the House of Windsor came just three months after people across Britain paused over a long holiday weekend to celebrate the queen’s 70 years on the throne. While crowds of cheering, flag-waving fans filled the streets around Buckingham Palace throughout four days of festivities, the queen herself made only two brief appearances on the palace balcony to wave to her subjects.

Elizabeth has increasingly handed over duties to Charles and other members of the royal family in recent months as she recovered from a bout of COVID-19, began using a cane and struggled to get around.

Political leaders from across the spectrum joined Truss in expressing their concern, and Archbishop of Canterbury Justin Welby said the “prayers of the nation” were with Elizabeth.