The King stopped to greet crowds gathered outside Buckingham Palace as he arrived in London for the first time as monarch following the death of his mother.
Tearful and overwhelmed with emotion, people applauded and cheered the King during his 12-minute walkabout outside the palace gates, with several shouting "God bless you, Charles" and "God save the King".
One woman, Jenny Assiminios, even hugged and kissed the King on the cheek as he stopped in front of her, but the new monarch appeared to take it in his stride.
He shook hands with countless members of the public - the first to meet the King - thanking them for their good wishes, before he and his wife Camilla, the Queen Consort, walked into Buckingham Palace together.
The King will be proclaimed at the Accession Council at 10am tomorrow in the State Apartments of St James's Palace, Buckingham Palace has said - with the process televised for the first time in history.
Dressed in a black suit and tie, the grieving King left Balmoral this afternoon seated in the back of a car, with his wife in the front passenger seat, as they were driven to Aberdeen airport.
He stepped out carrying a bundle of papers and stopped to shake hands and spend time chatting to staff in the rain, before leaving on a plane bound for London.
The sun shone as the King arrived at RAF Northolt, still holding the file of papers, before being driven to Buckingham Palace.
The royal couple spent the night at Balmoral following the death of the 96-year-old monarch, who the King described as a "cherished sovereign and a much-loved mother".
The King held his first audience with Prime Minister Liz Truss at Buckingham Palace on Friday afternoon ahead of his televised national address at 6pm.
The 73-year-old was by his mother's side at her beloved Scottish Highlands home for much of Thursday after catching the royal helicopter from Dumfries House in Ayrshire.
Following news that the Queen's health was deteriorating, other senior royals also rushed to be by her side, including the next in line to the throne, Prince William.
His brother, Prince Harry, was the first to leave the Royal Family's Scottish residence this morning, and boarded a British Airways flight from Aberdeen to London, after he travelled to Scotland alone.
Prince William did not join his father, as it is royal protocol that the monarch and heir to the throne do not travel together.
He later left Balmoral to travel back to Windsor to be with his wife, the Duchess of Cornwall and Cambridge, and their children, princes George and Louis, and Princess Charlotte, who settled into their new school this week.
The Princess Royal, the Earl and Countess of Wessex and Prince Andrew remain in Scotland.
Senior royals will have duties to perform in Scotland in the coming days when the Queen's coffin begins its journey back to the capital.
King Charles III acceded to the throne immediately following the death of Elizabeth II on Thursday, and described losing his mother as "a moment of the greatest sadness for me and all members of my family".
During this period of mourning, he said he and his family would be "comforted and sustained by our knowledge of the respect and deep affection in which the Queen was so widely held".
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The new monarch - born Charles Philip Arthur George - became heir to the throne at the age of three, a title he would hold for 70 years.
He has been preparing to be King for his entire life, and has chosen to use his Christian name for his title as monarch, just like his late beloved mother, Queen Elizabeth II.
The formal process of proclaiming him King, will be carried out by the Accession Council - a group made up of Privy Counsellors, Great Officers of State, the Lord Mayor of London, Realm High Commissioners and senior civil servants.
It is split into two parts. The first approves various consequential orders including the arrangements, without the King present.
The second involves the King holding his first Privy Council, making his declaration and reading and signing an oath to uphold the security of the Church in Scotland (as unlike in England, Church and State are separate there) and approve orders which facilitate continuity of government.