Queen Elizabeth II, who reigned over Great Britain for 70 years -- the longest reign in the nation's history -- died at 96 at Balmoral Castle in Scotland on Thursday.
"The Queen died peacefully at Balmoral this afternoon," a statement posted late Thursday afternoon from Buckingham Palace read.
Earlier in the day, the palace had announced that the Queen been placed under medical supervision following "concern" from her doctors over her health.
Buckingham Palace released a statement from her eldest son Charles, who paid tribute to his "beloved Mother, Her Majesty The Queen."
"I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world," the statement said. "During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which The Queen was so widely held."
Elizabeth's last major constitutional action came Tuesday, when she accepted the resignation of Prime Minister Boris Johnson and asked his successor, Liz Truss, to form a new government.
The monarch appeared frail in a meeting with the newly appointed Prime Minister, and on Wednesday she canceled a virtual meeting with her Privy Council, based on doctors' orders advising rest, the New York Times reported.
Prince Charles, heir to the throne, and Prince William, the Duke of Cambridge, along with other members of her family, traveled to Balmoral on Thursday to be by her bedside, the Washington Post reported.
When Queen Elizabeth became queen in 1952 as a young mother following the death of her father, she had this to say to her subjects: "I declare before you all that my whole life, whether it be long or short, shall be devoted to your service, and the service of our great imperial family to which we all belong."
White House Press Secretary Karine Jean-Pierre was conducting her daily briefing for reporters when news of the Queen's death broke.
"Our relationship with the people of the United Kingdom, and this is something that the president has said himself, has grown stronger and stronger. And it is one of our closest allies," she said, the Times reported. "And, again, our hearts go to the people of the United Kingdom to the queen and to the family."
More information
Here is more on Queen Elizabeth and her reign.
SOURCE: Buckingham Palace, statement, Sept. 8, 2022; New York Times; Washington Post