The new King, Charles III renewed his mother's "lifelong promise of service" to the nation in a televised address from Buckingham Palace Friday evening.
King Charles paid tribute to his late mother the Queen, in an address to the nation, and spoke of his feelings of "profound sorrow".
He said she was "an inspiration" and an example to him and to his family.
He said hers was "a life well lived", adding she is "mourned most deeply in her passing".
I speak to you today with feelings of profound sorrow, says the King.
"I speak to you today with feelings of profound sorrow.
"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; for her love, affection, guidance, understanding and example."
The King says. "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."
"Alongside the personal grief that all my family are feeling, we also share with so many of you in the United Kingdom, in all the countries where The Queen was Head of State, in the Commonwealth and across the world, a deep sense of gratitude for the more than 70 years in which my Mother, as Queen, served the people of so many nations," says the King.
"In 1947, on her 21st birthday, she pledged in a broadcast from Cape Town to the Commonwealth to devote her life, whether it be short or long, to the service of her peoples.
"That was more than a promise: it was a profound personal commitment which defined her whole life."
She made sacrifices to duty, the King says. "Her dedication and devotion as Sovereign never waivered, through times of change and progress, through times of joy and celebration, and through times of sadness and loss."
King Charles III continues reflecting on his mother's service.
"In her life of service we saw that abiding love of tradition, together with that fearless embrace of progress, which make us great as Nations. The affection, admiration and respect she inspired became the hallmark of her reign.
"And, as every member of my family can testify, she combined these qualities with warmth, humour and an unerring ability always to see the best in people.
"I pay tribute to my mother's memory and I honour her life of service," says the King.
"I know that her death brings great sadness to so many of you.
"And I share that sense of loss beyond measure with you all."
Reflecting on her accession in 1952, the King says: "When The Queen came to the throne, Britain and the world were still coping with the privations and aftermath of the Second World War, and still living by the conventions of earlier times.
"In the course of the last 70 years we have seen our society become one of many cultures and many faiths.
"The institutions of the State have changed in turn. But, through all changes and challenges, our nation and the wider family of Realms - of whose talents, traditions and achievements I am so inexpressibly proud - have prospered and flourished.
"Our values have remained, and must remain, constant. The role and the duties of Monarchy also remain, as does the Sovereign's particular relationship and responsibility towards the Church of England - the Church in which my own faith is so deeply rooted.
"In that faith, and the values it inspires, I have been brought up to cherish a sense of duty to others, and to hold in the greatest respect the precious traditions, freedoms and responsibilities of our unique history and our system of parliamentary government."
The King is now speaking about his own reign, pledging to uphold her values.
"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.
"Wherever you may live in the United Kingdom or in the realms and territories across the world and whatever maybe your background and beliefs I shall endeavour to serve you with loyalty, respect and love, as I have throughout my life."
"My life will of course change as I take up my new responsibilities," says the King.
"It will no longer be possible for me to give so much of my time and energies to the charities and issues for which I care so deeply.
"But I know this important work will go on in the trusted hands of others.
"This is also a time of change for my family. I count on the loving help of my darling wife Camilla. In recognition of her own loyal public service since our marriage 17 years ago, she becomes my Queen Consort.
"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."
King Charles says that his son William will become Prince of Wales.
"As my heir, William now assumes the Scottish titles which have meant so much to me," he says.
"He succeeds me as Duke of Cornwall and takes on the responsibilities for the Duchy of Cornwall which I have undertaken for more than five decades.
"Today, I am proud to create him Prince of Wales, Tywysog Cymru, the country whose title I have been so greatly privileged to bear during so much of my life and duty.
"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."
In his speech King Charles III comments on his youngest son - the Duke of Sussex - and his wife.
"I express my love for Prince Harry and Meghan as they continue to build their lives overseas."
Speaking next about his mother's upcoming funeral, the King says: ""In a little over a week's time we will come together as a nation, as a Commonwealth and indeed a global community, to lay my beloved mother to rest.
"In our sorrow, let us remember and draw strength from the light of her example.
"On behalf of all my family, I can only offer the most sincere and heartfelt thanks for your condolences and support.
"They mean more to me than I can ever possibly express."
The King ends his address with the following words:
"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.
"Thank you for your love and devotion to our family and to the family of nations you have served so diligently all these years.
"May 'flights of Angels sing thee to thy rest'."