The new King took the throne following his mother's death at the age of 96 on Thursday afternoon.
Speaking during his proclamation ceremony in London, Charles said it was a "great consolation" to his family to see the outpouring of love for his mother.
He made a personal declaration on the death of the Queen saying: “I know how deeply you and the entire nation, and I think I may say the whole world, sympathise with me in this irreparable loss we have all suffered.”
He added: “Her reign was unequalled in its duration, its dedication and its devotion. Even as we grieve, we give thanks for this most faithful life.”
Vowing to serve the country as his mother did, Charles said: “I shall strive to follow the inspiring example I have been set in upholding constitutional government and to seek the peace, harmony and prosperity of the peoples of these islands, and of the Commonwealth realms and territories throughout the world.
"In carrying out the heavy task that has been laid upon me, and to which I now dedicate what remains to me of my life, I pray for the guidance and help of Almighty God."
When is the bank holiday for the Queen's funeral?
The Bank Holiday will be held on the same day as the funeral, which takes place at 11am on 19 September.
It will apply in England, Wales, Scotland and Northern Ireland.
Read more: The King’s address in full
Where is the funeral and who will attend?
The funeral will be held at Westminster Abbey in central London.
Many of the Queen's major life events have been held at the Abbey, including her marriage to the Duke of Edinburgh and her coronation in 1952.
The original plans are for the Queen’s coffin to process on a gun carriage to the abbey, pulled by naval ratings – sailors – using ropes rather than horses.
Senior members of the family are expected to follow behind – just like they did for the funeral of Diana, Princess of Wales and the Duke of Edinburgh.
The military will line the streets and also join the procession.
Heads of state, prime ministers and presidents, European royals and key figures from public life will be invited to gather in the abbey, which can hold a congregation of 2,000.
The service will be televised, and a national two minutes’ silence is expected to be held.
Where will the Queen be buried?
The same day as the funeral, the Queen’s coffin will be taken to St George’s Chapel at Windsor Castle for a televised committal service.
Later in the evening, there will be a private interment service with senior members of the royal family.
The Queen’s final resting place will be the King George VI memorial chapel, an annex to the main chapel – where her mother and father were buried, along with the ashes of her sister, Princess Margaret.
Philip’s coffin will move from the Royal Vault to the memorial chapel to join the Queen’s.