Queen Elizabeth has died peacefully at her Balmoral home in Scotland at the age of 96.
Her eldest son Charles is the new King to be known as Charles III.
In a statement the 73-year-old monarch said: “The death of my beloved Mother, Her Majesty The Queen, is a moment of the greatest sadness for me and all members of my family.”
“We mourn profoundly the passing of a cherished Sovereign and a much-loved mother. I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world.”
King Charles and his wife Camilla, the Queen consort, will return to London today after gathering with other members of the family at Balmoral.
He is expected to speak to the nation on his return.
News that the Queen’s health was rapidly deteriorating emerged shortly after midday on Thursday when her doctors said she was under medical supervision, prompting her family to rush to Scotland to be by her side.
She had been suffering from what Buckingham Palace called “episodic mobility problems” since the end of last year, forcing her to withdraw from nearly all her public engagements.
Her last public duty was on Tuesday, when she appointed Liz Truss prime minister, the 15th of her reign.
Flags across the nation are flying at half-mast and huge crowds have gathered at Buckingham Palace to pay their respects to the only head of state most had ever known.
Britain’s longest-reigning monarch was a symbol of stability and continuity for the United Kingdom and the Commonwealth during seven decades of dramatic change.
Queen Elizabeth II came to the throne following the death of her father King George VI on February 6, 1952, when she was just 25.
She was crowned in June the following year.
“I have in sincerity pledged myself to your service, as so many of you are pledged to mine. Throughout all my life and with all my heart I shall strive to be worthy of your trust,” she said on her coronation day.
During her reign, Queen Elizabeth witnessed massive political, social and technological change.
Her own family’s trials and tribulations were played out in full public glare and re-enacted in movies and TV series.
She never gave a media interview out of respect for the monarchy.
The Queen leaves a large and devoted family that only last year mourned the death of her husband of 73-years Prince Philip.
Her four children, Charles, Anne, Andrew and Edward, gave her eight grand-children. She also leaves 12 great-grandchildren.
Prince William has become the heir to the throne at the age of 40.
The Royal Family will now enter a period of mourning with all official engagements cancelled.