Her Majesty Queen Elizabeth II has died at the age of 96, Buckingham Palace has announced.
In a statement, Buckingham Palace said: "The Queen died peacefully at Balmoral this afternoon.
"The King and the Queen Consort will remain at Balmoral this evening and will return to London tomorrow."
The Queen's family had gathered at her Balmoral residence in Scotland on Thursday afternoon.
Earlier, the Palace had released a statement saying the Queen was under medical supervision at Balmoral after doctors became concerned for her health.
The Queen came to the throne in February 1952 upon the death of her father King George VI.
Her 70-year reign was the longest in the history of the United Kingdom.
The Queen's Platinum Jubilee was marked earlier this year with celebrations around the Commonwealth.
Her eldest son Charles, 73, will now become King Charles III and will lead the country in mourning as head of state for 14 Commonwealth realms.
In a statement, he said: "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.
During the coming period of mourning, he said he and his family would be "comforted and sustained by our knowledge of the respect and deep affection in which the Queen was so widely held".
Camilla, Duchess of Cornwall, will become Queen Consort.
In a statement outside 10 Downing Street, Liz Truss, the Prime Minister, said: "We are all devastated by the news we have just heard from Balmoral.
"The death of Her Majesty the Queen is a huge shock to the nation and to the world.
"Queen Elizabeth II was the rock on which modern Britain was built. Our country has grown and flourished under her reign. Britain is the great country it is today because of her.
"She ascended the throne just after the Second World War, she championed the development of the Commonwealth from a small group of seven countries to a family of 56 nations spanning every continent of the world.
"We are now a modern thriving dynamic nation. Through thick and thin, Queen Elizabeth II provided us with the stability and the strength that we needed.
"She was the very spirit of Great Britain and that spirit will endure.
"She has been our longest ever reigning monarch. it is an extraordinary achievement to have presided with such dignity and grace for 70 years.
"Her life of service stretched beyond most of our living memories. In return she was loved and admired by people in the United Kingdom and all around the world.
"She has been a personal inspiration to me and to many Britons. Her devotion to duty is an example to us all.
"Earlier this week, at 96, she remained determined to carry out her duties, as she appointed me as her 15th Prime Minister.
"Throughout her life she has visited more than 100 countries and she has touched the lives of millions around the world.
"in the difficult days ahead we will come together with our friends across the United Kingdom, the Commonwealth and the world, to celebrate her extraordinary lifetime of service. It is a day of great loss but Queen Elizabeth II leaves a great legacy.
"Today the Crown passes as it has done for more than 1000 years to our new monarch, our new Head of State, King Charles III.
"With the King's family, we mourn the loss of his mother, and as we mourn, we must come together a people to support him, to help him bear the awesome responsibility that he now carries for us all.
"We offer him our loyalty and devotion just as his mother devoted so much to so many for so long, and with the passing of the second Elizabethan age, we usher in a new era in the magnificent history of our great country, exactly as Her Majesty would have wished, by saying the words, God Save the King."
Sir Keir Starmer, Leader of the Opposition, said: "Today we mourn the passing of a remarkable sovereign.
"It is a deep, private loss for the Royal Family and all our thoughts are with them at this time.
"The nation shares in their grief.
"We will always treasure Queen Elizabeth II's life of service and devotion to our nation and the Commonwealth; our longest-serving and greatest monarch.
"Above the clashes of politics, she stood not for what the nation fought over, but what it agreed upon.
"As Britain changed rapidly around her, this dedication became the still point of our turning world.
"So as our great Elizabethan era comes to an end, we will honour the late Queen's memory by keeping alive the values of public service she embodied.
"For seventy years, Queen Elizabeth II stood as the head of our country. But in spirit, she stood amongst us."
At Buckingham Palace, crowds gathered throughout the afternoon amid concerns for the Queen's health.
People began crying as they heard of the Queen's death.
The Union flag on top of the palace was lowered to half-mast at 6.30pm.
The Queen was born Elizabeth Alexandra Mary Windsor, in Mayfair, London, on April 21 1926, the eldest daughter of the Duke and Duchess of York, later King George VI and Queen Elizabeth.
When her uncle, King Edward VIII, abdicated in 1936 and her father became King, she became the heir to the throne.
She married Philip, Prince of Greece, in 1947. They had four children, Charles, Anne, Andrew and Edward, eight grandchildren and 12 great grandchildren.
Following her father's death in 1952, her Coronation took place in 1953.
She marked her Silver Jubilee in 1977, her Golden Jubilee in 2002, and her Diamond Jubilee in 2012.
Her mother, Queen Elizabeth the Queen Mother, and her sister Princess Margaret, died in 2002.
Prince Philip, Duke of Edinburgh, died in 2021, aged 99.
New parking system set to launch at Royal Lancaster Infirmary
Museum in Lancaster up for award launched by TV historian David Olusoga
MP fights for refunds after Heysham medical centre patients get parking fines in error
Two teenagers arrested after car stolen during Hest Bank burglary
Parents demand further action after health watchdog probe into asbestos complaints at Lancaster school
Lancaster medical students praised for helping man who collapsed
Man arrested on Morecambe beach after report of assault
Police probe burglaries in villages near Carnforth
Swift success as Lancaster councillors agree further help for endangered birds
Emergency services called to crash on M6 near Lancaster
Popular Morecambe eatery announces ‘difficult decision’ to close
Heartbreaking decision for family as Morecambe gift shop closure announced
Lancaster University PhD student off to Australia and New Zealand to tackle 'silent crisis'
PHOTO: Stolen pick up truck pulled from River Lune in Lancaster
LISTEN: Cyclists aim to raise £18,000 in 24-hour Lancaster challenge through pedal power
Award-winning Lancashire fire search dog who helped with earthquake rescues retires
Firefighters called to business park in Lancaster
Lancaster pupils turn 'creative history detectives' to celebrate life of art pioneer
Delight at Morecambe social club as theme park legend Frontier Fred drops in
Roads closed as gas mains upgrade work underway in Lancaster
