Speaking for the first time as monarch from Buckingham Palace, the 73-year-old thanked his “darling mama” for her “love and devotion to our family and to the family of nations”.
“May flights of angels sing thee to thy rest,” Charles, wearing a black suit and tie, said in an emotional address - in a quote from Hamlet.
“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.”
As Charles spoke, dignitaries attended a sombre remembrance service for the late queen at St Paul’s Cathedral that saw the first official rendition of the updated national anthem “God Save the King”.
Earlier, the oldest heir to ascend to the throne received flowers, cheers and even kisses as he greeted well-wishers outside Buckingham Palace on his return from Scotland, where his mother died “peacefully” aged 96 on Thursday.
“He’s got a hard act to follow,” Londoner Stephen Johnson, 56, told AFP, standing by the palace’s railings holding a Union Jack flag and photo of the queen. “He’s our king now, we’ve got to love him.”
Church bells and ceremonial gun salutes for the departed monarch had sounded across a country dealing with the loss of a constant presence for the last 70 years.
Charles - who held his first audience with British Prime Minister Liz Truss as monarch - will be formally proclaimed king to the public at 10:00am GMT (4pm Phuket time) today.
In his address, he said his elder son William, who moves up the line of succession to become heir, would become the new Prince of Wales.
William’s wife Kate will also assume the title of Princess of Wales once held by his mother Princess Diana, who died in 1997.
Charles also expressed his “love” for his younger son Harry and Harry’s wife Meghan who has levelled damaging criticisms against the royal family as the couple broke away to start a new life in the US.
Elizabeth II reigned for a record-breaking 70 years, a source of stability in a period of extraordinary change whose death sparked heartfelt tributes from across the world.
The new king and other members of the royal family will observe an extended mourning period from yesterday until seven days after her funeral.
The date of the funeral, which will be attended by heads of state and government, has yet to be officially announced but is expected to be on Monday, September 19.
While Britons adjusted to the shock of the departure of their only head of state since the aftermath of World War II, tributes poured in for one of the planet’s most recognisable people.
Flowers were also left at British embassies around the world, including in Moscow - currently at odds with London over the war in Ukraine.
‘Sense of duty’
Buckingham Palace in London became the epicentre for thousands of mourners, with flowers piling up in a sign of the reverence felt for the queen.
“I came to say a prayer,” said Joan Russell, a 55-year-old project manager from northeast London, with tears running down her cheeks as she looked at the tributes lining the gates.
“She has been our monarch all my life and she has led by example, she has learnt, she has listened, wherever you go, she is our stamp,” she added, noting “Charles has had such a great example to follow”.
Premier Truss offered the nation’s support to Charles as she said he now bore an “awesome responsibility” at the start of two days of special tributes to his mother in parliament.
“Even as he mourns, his sense of duty and service is clear,” she said.
Truss lavished praise on the queen as “one of the greatest leaders the world has ever known”.
“Her legacy will endure through the countless people she met, the global history she witnessed and the lives that she touched,” the premier said.
While the government has said there is no obligation on organisations to suspend business during the period of national mourning, many are doing so as a mark of respect.
The Premier League postponed all matches this weekend, the TUC umbrella body of trade unions postponed its congress due to begin tomorrow, while railway and postal workers halted upcoming strikes over pay, as Britain is gripped by soaring inflation and spiralling energy prices.
Elizabeth’s public appearances had become rarer in the months since she spent an unscheduled night in hospital in October 2021 for undisclosed health tests.
She was seen smiling in her last official photographs from Tuesday when she appointed Truss as the 15th prime minister of her reign, which started with Winston Churchill in Downing Street.
But the queen, visibly thinner and stooped, leant on a walking stick. Her hand was also bruised dark blue-purple, sparking concern.
Jane Barlow, the photographer who took the last public pictures of the queen on Tuesday, said she was “frail” but in “good spirits”.
The queen’s closest family members had rushed to be at her bedside Thursday at Balmoral, a private residence set among thousands of acres of rolling grouse moors and forests in the Scottish Highlands.
However, some of her closest relatives - sons Andrew and Edward, and grandsons William and Harry - arrived after she had died that afternoon.
Her body is expected to remain there initially before being taken tomorrow to the Palace of Holyroodhouse in Edinburgh.
From the Scottish capital, her coffin is due to travel to London on Tuesday for a lying in state accessible to the public.
Officials expect more than one million people to file past the catafalque in Westminster Hall, the oldest part of the parliamentary complex, before the televised funeral service at Westminster Abbey opposite.
Queen Elizabeth II came to the throne aged just 25 in the exhausted aftermath of World War II, joining a world stage dominated by political figures from Churchill to Mao Zedong and Joseph Stalin.
In the ensuing decades, the last vestiges of Britain’s vast empire crumbled.
At home, Brexit shook the foundations of her kingdom, and her family endured a series of scandals.
But throughout, she remained consistently popular and was head of state not just of the United Kingdom but 14 former British colonies, including Australia and Canada.
New Zealand proclaimed Charles its new king. But Australia’s new government looks set to revive a push to ditch the monarchy, casting doubt on his inheritance even as it mourns the queen.
The final public farewell at Westminster Abbey in London will be a public holiday in the form of a Day of National Mourning.
Charles’s coronation, an elaborate ritual steeped in tradition and history, will take place in the same historic surroundings, as it has for centuries, on a date to be fixed.