King Charles III has given his eldest son William and daughter-in-law Catherine the titles of Prince and Princess of Wales, which he and his late wife Diana previously held.
Delivering his first speech since the death of his mother Queen Elizabeth II on Thursday (local time), Charles said he was proud to make his heir William the Prince of Wales, a title Charles had held since 1958.
"Today, I am proud to create him Prince of Wales, the country whose title I have been so greatly privileged to bear, during so much of my life and duty," the King said.
"With Catherine 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."
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.
In his address, the King expressed his "love for Harry and Meghan" and said he supports them as they "continue to build their lives overseas".
Diana died in a car crash in 1997 aged 36, five years after she and Charles separated.
Charles III shook hands with well-wishers outside Buckingham Palace ahead of his address, in which he spoke with "profound sorrow" about his mother.
"Queen Elizabeth was a life well lived, a promise of destiny kept, and she is mourned most deeply in her passing," he said.
"My beloved mother was an inspiration and example to me, and to all my family. And we owe her the most heartfelt debt any family could owe to their mother, for her love, affection, guidance, understanding and example."
King Charles III and Queen Consort Camilla had boarded a plane at Aberdeen Airport and returned to Buckingham Palace, where he met with newly appointed Prime Minister Liz Truss ahead of his address.
The United Kingdom has declared 10 days of national mourning ahead of the Queen's funeral, to be held at Westminster Abbey in London.
The Queen, who was 96, died at Balmoral just after 6:30pm on Thursday local time (3:30am Friday AEST), hours after her doctors said they were "concerned" for her health.
She was the United Kingdom's longest-reigning monarch, serving 70 years on the throne with 15 prime ministers.
Official proclamation
The King will be officially proclaimed the new monarch of Britain and the Commonwealth at a meeting of the Accession Council at St James's Palace on Saturday at 10:00am local time (7:00pm AEST), Buckingham Palace said.
The meeting proclaims the new sovereign and sees the King sign an oath to uphold the security of the Church in Scotland.
Following the meeting, there will be the Principal Proclamation from the balcony overlooking Friary Court at St James's Palace, with other announcements of the new monarch made across the United Kingdom and in the City of London.
In an earlier statement, King Charles said the death of his mother was a "moment of the greatest sadness for me and all members of my family".
"I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world," he said.
Bells tolled at churches across England and Scotland 96 times — the number of years of the Queen's life — from Westminster Abbey and St Paul's Cathedral in London to Windsor Castle.
Prime Minister Anthony Albanese spoke with Ms Truss over the phone, extending his condolences to the government and people of the United Kingdom.
"Prime Minister Albanese offered sincere condolences to the government and people of the United Kingdom and Prime Minister Truss gave her condolences to all Australians at this sad time," a statement from Mr Albanese's office said.
"The two leaders spoke about Queen Elizabeth II's remarkable life, legacy and dedication to duty."
King Charles III's eldest son and heir Prince William, the Duke of Cambridge, has also left Balmoral and returned to Windsor.
Meanwhile, preparations are underway to transport the Queen's body to nearby Aberdeen, Scotland for her final journey back to Buckingham Palace in London.
After the Queen's body is taken to Aberdeen, it will then be loaded onto the Royal Train for a journey down Scotland's east coast to Edinburgh.
Kilted soldiers will form guards of honour at stations along the way, and mourners are expected to line the route.
In Edinburgh, the Queen's coffin will lie at the official royal residence, Holyroodhouse, for a day.
The next day, it will then be carried in procession through Edinburgh's historic centre, up the Royal Mile to the ancient St Giles' Cathedral, near Edinburgh Castle.
After the ceremonies in Scotland finish, the Queen's body will be put back on the Royal Train from Edinburgh's Waverley station to St Pancras in London.
Members of the armed forces and emergency services will form an honour guard on every platform of the route.
Large crowds are expected to gather and the train is expected to travel slowly down the East Coast Main Line to allow people to pay their respects and share tributes.
Her body is then expected to be taken to Buckingham Palace's throne room before lying in state for four days at Westminster Hall.
ABC/Wires
