The King paid a heartfelt tribute to his "darling Mama" on Friday and, in a historic television address, pledged his life to serving the nation as she had done.
Sitting at a mahogany desk beside a photograph of the Queen that he had chosen from Clarence House, Charles III appeared close to tears at times - praising his late mother as an inspiration and an example to all of his family.
He said: “We owe her the most heartfelt debt any family can owe to their mother; for her love, affection, guidance, understanding and example.
“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.
“Thank you for your love and devotion to our family and to the family of nations you have served so diligently all these years."
In a final flourish borrowed from Shakespeare’s Hamlet, he added: "May ‘flights of Angels sing thee to thy rest’."
In Act 5 Scene 2 of Hamlet, Horatio holds his dying friend in his arms and pays tribute to the Prince of Denmark, saying: “Now cracks a noble heart. Good night, sweet prince, and flights of angels sing thee to thy rest”.
The line is often used as a mark of respect when someone dies.
His "angels" sign-off also featured in musical composition Song for Athene, by John Tavener and performed at Diana’s funeral in 1997.
The King’s emotional address, his first to the nation and the Commonwealth as monarch, was seen by millions around the UK and the world.
MPs watched the speech in silence in the House of Commons chamber, some visibly wiping away tears, before applauding at the end of the address.
The nine and a half minute broadcast had been recorded on Friday afternoon in the Blue Drawing Room at Buckingham Palace where the late Queen Elizabeth II delivered several of her Christmas messages.
The King echoed the vow that his mother had made on her 21st birthday - to devote his whole life, however long it may be, to service.
His Majesty added: “That promise of lifelong service I renew to you all today.
“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.”
The monarch used his address to make William and Kate the new Prince and Princess of Wales, an honour not always accorded to the heir to the throne immediately.
He also offered an olive branch to the estranged Duke and Duchess of Sussex, expressing his "love for Harry and Meghan as they continue to build their lives overseas".
The King, dressed in a black suit, white shirt, black tie and with a black and white checked handkerchief in his breast pocket, paid tribute to his "darling wife" Camilla, the new 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."
He vowed to retain the monarchy’s devotion to the Church of England and its values.