LONDON — Queen Elizabeth II, Britain’s longest-serving monarch, whose broadly popular seven-decade reign survived tectonic shifts in her country’s post-imperial society and weathered successive challenges posed by the romantic choices, missteps and imbroglios of her descendants, died on Thursday at Balmoral Castle in Scotland, her summer retreat. She was 96.

Queen Elizabeth II Dies at 96 Was Britain’s Longest-Reigning Monarch

The royal family announced her death online, saying she had “died peacefully.” The announcement did not specify a cause.

Her death elevated her eldest son, Charles, to the throne, as King Charles III. In a statement, he said:

“The death of my beloved Mother, Her Majesty the Queen, is a moment of the greatest sadness for me and all members of my family.

“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.”

Earlier Thursday, Buckingham Palace said that the queen had been placed under medical supervision and that her doctors were “concerned” about her health. She had remained at Balmoral for much of the summer. On Wednesday evening, she abruptly canceled a virtual meeting with members of her Privy Council after her doctors advised her to rest.

On Tuesday, she met with the incoming Conservative prime minister, Liz Truss — the 15th prime minister the queen dealt with during her reign — though in doing so, because of infirmity, she broke with longstanding tradition by receiving her at Balmoral rather than at Buckingham Palace.

Elizabeth’s long years as sovereign were a time of enormous upheaval, in which she sought to project and protect the royal family as a rare bastion of permanence in a world of shifting values.Queen Elizabeth II Dies

At her coronation on June 2, 1953, a year after she acceded to the throne, she surveyed a realm emerging from an empire of such geographical reach that it was said the sun never set on it. But by the new century, as she navigated her advancing years with increasing frailty, the frontiers had shrunk back. As Britain prepared to leave the European Union in 2020, a clamor for independence in Scotland was rekindled, potentially threatening to narrow her horizons yet further.

Her coronation was the first royal event of its kind to be broadcast almost in full on television. But it was a token of the changes — and global fascination — that accompanied her time as queen that her reign became the subject of a Hollywood movie and a blockbuster series on Netflix, while her family’s travails offered voluminous grist to the busy mill of social media.

Just as telling in the chronicles of her rule, Britons’ unquestioning deference to the crown had been supplanted by a gamut of emotions ranging from loyal and often affectionate tolerance to unbridled hostility. The monarchy was forced, more than ever, to justify its existence in the face of often skeptical public attention and scrutiny.

Elizabeth, though, remained determinedly committed to the hallmark aloofness, formality and pageantry by which the monarchy has long sought to preserve the mystique that underpinned its existence and survival. Her courtly and reserved manner changed little.

As the coronavirus pandemic of 2020 spread to Britain, forcing people to suspend their normal lives and social ways, the queen left Buckingham Palace, in central London, for Windsor Castle, west of the capital, a move that recalled the decades she had spent inspiring genuine affection among many Britons.

It was to Windsor that she and her younger sister, Margaret, were sent to escape the threat of German bombing after the outbreak of World War II in 1939. It was from Windsor, too, that she made her first radio broadcast as a princess in 1940, age 14, ostensibly directed at British children who had been evacuated to North America, according to her biographer Ben Pimlott, but also intended to sway official thinking in Washington, which had not yet entered the war.

“My sister, Margaret Rose, and I feel so much for you, as we know from experience what it means to be away from those we love most of all,” Elizabeth said then.

Queen Elizabeth II Dies at 96 Was Britain’s Longest-Reigning Monarch

In 2020, too, she sought to equate her plight with that of her subjects. “Many of us will need to find new ways of staying in touch with each other and making sure that loved ones are safe,” she said in a statement released after she and her husband, Prince Philip, arrived at Windsor. “I am certain that we are up to that challenge. You can be assured that my family and I stand ready to play our part.”Queen Elizabeth II Dies

On April 5, 2020, in a televised address that evoked her 1940 broadcast, she urged her subjects to fight the virus with the same bulldog tenacity that wartime Britons had shown. It was only the fourth special broadcast of her monarchy outside of her scheduled TV appearances at Christmas.

“I hope in the years to come everyone will be able to take pride in how they responded to this challenge,” she said. “And those who come after us will say that the Britons of this generation were as strong as any.”

She added, “We should take comfort that while we may have more still to endure, better days will return. We will be with our friends again; we will be with our families again; we will meet again,” the last line a direct reference to a wartime song by Vera Lynn, “We’ll Meet Again.”

In 2017, Elizabeth celebrated the 70th anniversary of her marriage to Philip, whom she first met when he was a teenager in the 1930s. Until his death last April, Philip had settled into an unusual role, usually two steps behind his wife, providing her with stoic support, even if his occasional tactless comments hurt his image.

Despite many reports of early peccadilloes on Philip’s part — hidden from public view with the help of cooperative newspaper barons — their bonds endured, a throwback to earlier decades of more durable relationships. And his death, their second son, Prince Andrew, said, “left a huge void in her life.”

Some predicted that Elizabeth would recede into the shadows after Philip’s death, much as Queen Victoria did after the death of her husband, Prince Albert. But she surprised many by re-emerging as a spry presence in public life, entertaining world leaders at a summit meeting in Cornwall in June 2021 and playing host to Bill Gates and other businesspeople at Windsor Castle after a climate-change investment conference.

Still, the hectic schedule took a toll. Elizabeth was photographed using a walking stick, a rare concession to her stiff knees. She was kept overnight in a London hospital in October 2021 after what aides said was an episode of exhaustion. Few doubted the effect of the loss of Philip, who had been a stabilizing force in the family.

Elizabeth’s own children seemed less immune to marital calamity. Queen Elizabeth II Dies

In 1992, Prince Charles and his immensely popular wife, Diana, agreed to separate, as did Prince Andrew and his wife, Sarah Ferguson. Elizabeth’s second child, Princess Anne, divorced her husband, Mark Phillips, the same year. Coupled with a series of other upheavals, the queen labeled 1992 her “annus horribilis.”

But worse was to come.

In 1997, the death of Diana in a car crash in Paris wrote some of the darkest chapters of Elizabeth’s reign, and for a while the monarchy itself seemed threatened by a huge wave of public support for Diana that left the queen seeming cold and emotionally estranged from her subjects.

The monarchy survived, but well into the 21st century new challenges emerged.

In 2019, Elizabeth was dragged unceremoniously and against all previous rules of protocol into political machinations over Brexit, as Britain’s withdrawal from the European Union was known, a debate from which she would once have remained remote.

In the same year, Prince Andrew became embroiled in scandal after giving a disastrous television interview in which he seemed unaware of the toxic impact of a friendship with Jeffrey Epstein, the convicted American sexual predator. Accused of sexual impropriety with a teenage girl introduced to him by Mr. Epstein — an allegation he has denied — the prince, also known as the Duke of York, withdrew from public life that November. (In January this year, he was forced by Buckingham Palace to relinquish his military titles and royal charities, a stinging rebuke by the royal family a day after a federal judge in New York allowed a sexual abuse case against him to go ahead.)

In her annual Christmas address to the nation in 2019, the queen described the year as “bumpy.”

It was about to get bumpier. Queen Elizabeth II Dies