Charles, who spent much of his 73 years preparing for the role of king, addressed a nation grieving the only British monarch most people alive today had ever known. He takes the throne in an era of uncertainty for both his country and the monarchy itself.
He spoke of his “profound sorrow” over the death of his mother, calling her an inspiration.
“That promise of lifelong service I renew to all today,” he said in the recorded, 9 1/2-minute address, delivered with a framed photo of the queen on a desk in front of him.
“As the queen herself did with such unswerving devotion, I, too, now solemnly pledge myself, throughout the remaining time God grants me, to uphold the constitutional principles at the heart of our nation," he said.
The king's speech was broadcast on television and streamed at St. Paul’s Cathedral, where some 2,000 people attended a service of remembrance for the queen. Mourners at the service included Prime Minister Liz Truss and members of her government.
As the country began a 10-day mourning period, people around the globe gathered at British embassies to pay homage to the queen, who died Thursday at Balmoral Castle in Scotland.
In London and at military sites across the United Kingdom, cannons fired 96 shots in an elaborate, 16-minute salute marking each year of the queen’s life.
In Britain and across its former colonies, the widespread admiration for Elizabeth herself was occasionally mixed with scorn for the institution and the imperial history she symbolized.
On the king's first full day of duties, Charles left Balmoral and flew to London for a meeting with Truss, appointed by the queen just two days before her death.
He arrived at Buckingham Palace, the monarch's London home, for the first time as sovereign, emerging from the official state Bentley limousine alongside Camilla, the queen consort, to shouts from the crowd of “Well done, Charlie!” and the singing of the national anthem, now called “God Save the King.” One woman gave him a kiss on the cheek.
Under intense scrutiny and pressure to show he can be both caring and regal, Charles walked slowly past flowers heaped at the palace gates for his mother. The mood was both grieving and celebratory.
As the second Elizabethan Age came to a close, hundreds of people arrived through the night to grieve together outside the gates of Buckingham Palace and other royal residences, as well as British embassies worldwide. Some came simply to pause and reflect.
Finance worker Giles Cudmore said the queen had “just been a constant through everything, everything good and bad.”
At Holyrood Palace in Edinburgh, mourner April Hamilton stood with her young daughter, struggling to hold back tears.
“It’s just such a momentous change that is going to happen,” she said. “I’m trying to hold it together today.”
Everyday politics was put on hold, with lawmakers paying tribute to the monarch in Parliament over two days, beginning with a special session where Truss called the queen “the nation’s greatest diplomat.”
Senior lawmakers will also take an oath to King Charles III.
Meanwhile, many sporting and cultural events were canceled as a mark of respect, and some businesses — including Selfridges department store and the Legoland amusement park — shut their doors. The Bank of England postponed its meeting by a week.
But while Elizabeth’s death portends a monumental shift for some, day-to-day life in Britain went on in other respects, with children in school and adults at work, facing concerns about inflation.
Charles, who became the monarch immediately upon his mother's death, will be formally proclaimed king at a special ceremony Saturday. The new king is expected to tour the United Kingdom in the coming days.
The queen's coffin will be brought to London, where she is expected to lie in state before a funeral at Westminster Abbey, expected around Sept. 19.
Elizabeth was Britain’s longest-reigning monarch and a symbol of constancy in a turbulent era that saw the decline of the British empire and disarray in her scandal-plagued family.
The impact of Elizabeth's loss will be unpredictable. The public’s abiding affection for the queen had helped sustain support for the monarchy during the family scandals, including the divorce of Prince Charles and Princess Diana, but Charles does not command that kind of popularity.
“Charles can never replace her, you know," said 31-year-old Londoner Mariam Sherwani.
Like many, she referred to Elizabeth as a grandmother figure. Others compared her to their mothers, or great-grandmothers.
But around the world, her passing revealed conflicting emotions about the nation and institutions she represented.
In Ireland, some soccer fans cheered.
In India, once the “jewel in the crown” of the British empire, entrepreneur Dhiren Singh described his own personal sadness at her death, but added, “I do not think we have any place for kings and queens in today’s world."
For some, Elizabeth was a queen whose coronation glittered with shards of a stunning 3,106-carat diamond pulled from grim southern African mines, a monarch who inherited an empire they resented.
In the years after she became queen, tens of thousands of ethnic Kikuyu in Kenya were rounded up in camps by British colonizers under threat from the local Mau Mau rebellion. Across the continent, nations rejected British rule and chose independence in her first decade on the throne.
She led a power that at times was criticized as lecturing African nations on democracy but denying many of their citizens the visas to visit Britain and experience it firsthand.
While the global fascination with the British queen is puzzling to some, others felt a personal connection to a woman who seemed ubiquitous, from banknotes used on multiple continents to TV shows like “The Crown" — which is pausing production to honor her.
Adi Trivedi, a 33-year-old British lawyer living in Paris, called Elizabeth “a model of humility, a model of duty, taking the ego out of an office of state.” He hopes to join the mourners at Buckingham Palace soon, so that "we can really celebrate the life of Queen Elizabeth II together.”