King Charles has vowed to serve the people of the United Kingdom with "loyalty, respect, and love" during his first televised address to the nation.
Offering words of comfort following the death of his mother, Queen Elizabeth II, the King paid tribute to her "love, affection, guidance, understanding and example" in a speech from Buckingham Palace.
"Queen Elizabeth was a life well lived; a promise with destiny kept and she is mourned most deeply in her passing. That promise of lifelong service I renew to you all today," he said.
"Throughout her life, Her Majesty The Queen - 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 can owe to their mother."
A memorial service for the Queen has been held at St Paul's Cathedral, with 2,000 members of the public joining politicians, including the prime minister, to watch the King's address.
Speaking from the Blue Drawing Room of the palace, where his mother recorded some of her Christmas messages, the monarch dedicated part of his speech to other senior royals, including his wife and children.
Of Camilla, now the Queen Consort, he said: "I know she will bring to the demands of her new role the steadfast devotion to duty on which I have come to rely so much."
Speaking about his eldest son Prince William, who is now the Duke of Cornwall, Prince of Wales and heir to the throne, the King said he would "continue to inspire" alongside his wife, Catherine.
He expressed his love for the Duke and Duchess of Sussex, Harry and Meghan "as they continue to build their lives overseas" - in what could be considered a symbol of his bid for reconciliation amid past troubles with the couple.
As he begins his reign, the King also set out his changing role, saying it will "no longer be possible" for him to give as much "time and energies to the charities and issues" he cares "so deeply" about.
'To my darling Mama...'
King Charles sat to deliver his address, with a posy of sweet peas mixed with rosemary placed on a desk in front of him, which represents remembrance.
"On behalf of all my family, I can only offer the most sincere and heartfelt thanks for your condolences and support," the King said.
"They mean more to me than I can ever possibly express.
"And to my darling Mama, as you begin your last great journey to join my dear late Papa, I want simply to say this: thank you."
He thanked the Queen for her "love and devotion" before concluding his address with a quote from the William Shakespeare play Hamlet.
"May 'flights of Angels sing thee to thy rest'," His Majesty said.
Monarch already carrying out royal duties
The address was broadcast after King Charles was seen meeting well-wishers waiting outside Buckingham Palace.
He shook hands with dozens of people, and was also hugged and kissed before walking through the palace gates with his wife by his side.
He returned to London with the Queen Consort, after spending Thursday at Balmoral to be with the Queen before she died.
Dressed in a black suit and tie, the grieving King left the royal residence seated in the back of a car, with his wife in the front passenger seat, as they were driven to Aberdeen airport.