King Charles III vows lifelong service in first address

King Charles III has pledged to follow his mother's example of "lifelong service" in his inaugural address to Britain and the Commonwealth, after ascending to the throne following the death of Queen Elizabeth II.

Speaking for the first time as monarch from Buckingham Palace on Friday, 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.

"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, Charles — 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.

Church bells and ceremonial gun salutes for the departed monarch rang out across the 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 11:00 am (1000 GMT) on Saturday.

READ MORE: 'End of an era': Reaction from world leaders to Queen Elizabeth's death

On William and Harry

In his address, the king 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.

"With Catherine (Kate) beside him, our new Prince and Princess of Wales will, I know, continue to inspire and lead our national conversations, helping to bring the marginal to the centre ground where vital help can be given," he said.

William and Kate, both 40, have taken on central roles within the royal family in recent years, appearing regularly in public and increasingly taking their three young children to events such as the queen's Platinum Jubilee earlier this year.

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.

"I want also to express my love for Harry and Meghan as they continue to build their lives overseas," the king said.

Extending mourning period

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.

Buckingham Palace said the king and other members of the royal family would observe an extended mourning period from now 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.

US President Joe Biden said he will attend the funeral. "I don't know the details yet, but I'll be going," he told reporters.

Biden spoke to media before boarding Air Force One at Columbus International Airport in Ohio, where he had been giving a speech.

READ MORE: In pictures: The life and times of Britain's Queen Elizabeth II