She died peacefully on Thursday afternoon at her Scottish estate, where she had spent much of the summer.

The Queen came to the throne in 1952 and witnessed enormous social change.

Her son King Charles III said the death of his beloved mother was a “moment of great sadness” for him and his family and that her loss would be “deeply felt” around the world.

He said: “We mourn profoundly the passing of a cherished sovereign and a much-loved mother.

“I know her loss will be deeply felt throughout the country, the realms and the Commonwealth, and by countless people around the world.”

During the coming period of mourning, he said he and his family would be “comforted and sustained by our knowledge of the respect and deep affection in which the Queen was so widely held”.

The King and his wife, Camilla, now Queen Consort, will return to London on Friday, Buckingham Palace said. He is expected to address the nation.

Senior royals had gathered at Balmoral after the Queen’s doctors became concerned about her health earlier in the day.

All the Queen’s children travelled to Balmoral, near Aberdeen, after doctors placed the Queen under medical supervision.

Her grandson and now heir to the throne, Prince William, and his brother, Prince Harry, also gathered there.

Prime Minister Liz Truss, who was appointed by the Queen on Tuesday, said the monarch was the rock on which modern Britain was built, who had “provided us with the stability and strength that we needed”.

Speaking about the new King, she said: “We offer him our loyalty and devotion, just as his mother devoted so much, to so many, for so long.

“And with the passing of the second Elizabethan age, we usher in a new era in the magnificent history of our great country, exactly as Her Majesty would have wished, by saying the words ‘God save the King’.”

The Archbishop of Canterbury Justin Welby – spiritual leader to the Church of England of which the monarch is supreme governor – expressed his “profound sadness”.

He said his “prayers are with the King and the Royal Family”.

Why was the Queen in Scotland?

Ever since her youth, Queen Elizabeth has spent most of her summers in Balmoral, a sprawling highland estate in Aberdeenshire, northeast Scotland. The castle was purchased by the royal family in 1852 under Queen Victoria’s reign. In a 2016 documentary, her granddaughter Princess Eugenie said the castle is where the Queen is “most happy.”

Clive Irving, author of Elizabeth II biography The Last Queen, says he believes The Queen had wanted to be in Scotland for the final months of her life. “Balmoral was always the one [royal residence] that had the qualities of a real home, compared to Windsor Castle and Buckingham Palace in particular, which is a soulless sort of place.”

How does the Queen’s death in Scotland change royal ceremony?

Official protocols for the Queen’s death, in place for decades, have been the subject of extensive leaks in the U.K. media over the years. The overarching plan is known as “Operation London Bridge,” and includes rules for everything from how the Prime Minister will be informed (“London Bridge is down”), to how King Charles III will address the nation, and what will happen to the Queen’s body.

That last part is more complicated since the Queen died in Scotland, a scenario that activated so-called “Operation Unicorn.” The Queen’s body will need to be moved from Balmoral to Holyroodhouse, her residence in the Scottish capital of Edinburgh, to lie in rest for a short time. The body will then be carried in a procession up the Royal Mile, a central avenue, to St. Giles Cathedral for a reception service.

What does the Queen’s death mean for Scotland’s relationship with the rest of the U.K.?

The transition of monarch from Elizabeth to her son, King Charles III, arrives at a tumultuous time for the union of the United Kingdom. Scotland’s semi-autonomous government is controlled by the Scottish National Party (SNP), which advocates for Scotland to become an independent country.

SNP leader Nicola Sturgeon has argued that the U.K.’s departure from the E.U., which Scottish voters opposed, means it is time for a new referendum on Scottish independence. (Scots voted down an independence referendum in 2014). Sturgeon insists a new poll should take place in 2024—though Truss, the new prime minister, has said she will block efforts to hold one.

Death of Queen Elizabeth II: The moment history stops

Across a life and reign, two moments from two very different eras illuminate the thread that bound the many decades together. At each a chair, a desk, a microphone, a speech. In each, that high-pitched voice, those clipped precise vowels, that slight hesitation about public speaking  that would never quite seem to enormous social change