Queen Elizabeth II has died at the age of 96.
Her eldest son, Charles, is now King.
Buckingham Palace released a statement just after 6:30pm on Thursday local time (3:30am Friday AEST), confirming the Queen had died at her Balmoral estate in the Scottish Highlands.
"The Queen died peacefully at Balmoral this afternoon," it read.
"The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow."
Charles, who will be known as King Charles III, issued a statement saying the death of his "beloved mother" was 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," he said.
"I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world.
"During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which The Queen was so widely held."
Britain's Prime Minister Liz Truss, who the Queen appointed on Tuesday, said the former monarch was "the rock on which modern Britain was built".
"Our country has grown and flourished under her reign," Ms Truss said.
"Britain is the great country it is today because of her."
During the Queen's 70 years on the throne, 15 prime ministers served and she held weekly private "audiences" with all except for Ms Truss.
What was said in those meetings was rarely publicised, and the views expressed by the Queen in those private meetings and the extent of the her political influence was often a subject of intense speculation.
Honour guard all the way to London
The Queen's body is expected to be taken from Balmoral to the nearby city of Aberdeen on Friday morning local time.
It will then be loaded onto the Royal Train for a journey down Scotland's east coast to the capital, Edinburgh.
Mourners are expected to line the route, and kilted soldiers will form guards of honour at stations along the way.
In Edinburgh, the Queen's coffin will lie at the official royal residence, a medieval palace called Holyroodhouse, for a day.
The Queen's body will then be carried in procession through Edinburgh's medieval heart, up the historic Royal Mile to the ancient St Giles' Cathedral, near Edinburgh Castle.
After the ceremonies in Scotland finish, the Queen's body will be put back on the Royal Train for a slow journey past huge crowds of mourners, including members of the armed forces and emergency services who will form an honour guard on every platform on the route to London's St Pancras station.
Her body is then expected to be taken to Buckingham Palace's throne room before lying in state for four days in Westminster Hall.
The UK has declared a period of 10 days of national mourning ahead of the Queen's funeral, which protocol says will be held at Westminster Abbey in London.
The Accession Council is expected to gather in the coming hours to proclaim Charles as the new sovereign.
That proclamation will be read out from a balcony at St James's Palace, as well as key locations across the United Kingdom and the Commonwealth.
King Charles will attend accession ceremonies in Scotland and Wales before returning to London to pay his final respects to his mother.
Royal website updated to reflect Charles's accession
The official website for the royal family, www.royal.uk, has been updated to pay homage to the Queen's life and reign and acknowledge Charles's accession to the throne as King.
Prior to the update, the website was black, and featured a picture of the Queen with the statement from the Buckingham Palace confirming her death.
A statement below it read: "The official website of the Royal Family is temporarily unavailable while appropriate changes are made."
The updates include biographies of newly crowned King Charles lll and Camilla, who is now the Queen Consort.
A condolence book has been added from which "a selection of messages will be passed on to members of the Royal Family".
Other updates include reflections on the Queen's early life, her hobbies and interests, family life and her role as the head of the Church of England.
Mourners gather outside Buckingham Palace
Crowds have gathered outside Buckingham Palace to lay flowers and pay their respects to the late monarch.
Just after 6:30pm local time (3:30am AEST) two members of the royal household came to the palace gates to post a notice announcing her death, and the flag that sits above it was lowered to half-mast.
Shortly after the announcement, mourners outside the palace broke out in a rendition of God Save The Queen, Britain's national anthem.
Standing outside the palace gates when the news was announced, Liberty Corrie, from Suffolk, said she broke down as soon as she heard.
"Me and my brother looked at each other, he was crying, I was crying, we were just in shock," she told the ABC.
"It was very surreal."
A line of London's iconic black cabs lined The Mall outside Buckingham Palace, forming a guard of honour for the former Queen, just as they had done after the death of Prince Philip.
Mark Colling, 53, from Dover, had just finished watching a show in the West End when he heard the news.
Walking along The Mall towards the palace to pay his respects, Mr Colling said he was "gutted".
"I've never known anyone else," he told the ABC.
"It's so sad. She's been brilliant."
'A moment in our history'
Prime Minister Anthony Albanese said he was shocked when he was woken by a telephone call from the Governor-General early this morning.
"And I think Australians this morning will have woken up with that shock as well because in our ever-changing world, Her Majesty's presence was a constant," Mr Albanese said.
Australia has now entered an official 10-day mourning period and parliament has been cancelled for next week according to formal procedures.
There was a 96-round salute at the front of Parliament House to symbolise every year of Queen Elizabeth's life.
Mr Albanese will travel to the UK with the Governor-General and Opposition Leader.
"This is a moment in our history," he said.
"For the whole of my life, I've only known one monarch, which is quite extraordinary."
Mr Albanese, who met the Queen at Buckingham Palace, said she had an exemplary devotion to duty.
Many other world leaders, including US President Joe Biden, have also offered their condolences and paid tribute to the Queen.
Downing Street said Ms Truss has spoken with Mr Albanese.
"The leaders shared their condolences following the passing of Her Majesty The Queen, and agreed she had touched the lives of many, both in Australia and the UK."
The Governor-General David Hurley formally addressed the nation on the passing of the Queen and remembered his last audience with the late monarch earlier this year via video.
"I will always treasure Linda's and my last call with Her Majesty, when we introduced the four Australians of the Year for 2022," he said.
"She was warm, funny and sincere in her interest in their work and our country.
"Her legacy will be profound. History will remember few like Queen Elizabeth II"
Health issues marked Queen's final years
The Queen reigned for more than 70 years, coming to the throne on the death of her father George VI in 1952.
She suffered a series of health issues in the years before her death, testing positive for COVID-19 in February 2022 and being forced to miss Platinum Jubilee events in June of that year because of what Buckingham Palace said were mobility issues.
Increasingly, she was forced to hand over public duties to younger members of the family, including Charles and his son Prince William, who is now next in line to the throne.
She also grieved for her husband Prince Philip, the Duke of Edinburgh, who died at the age of 99 in April 2021.
The couple spent much of his final year in isolation together at Windsor Castle amid the COVID pandemic.
Queen Elizabeth II is expected to be buried at King George VI Memorial Chapel in St George's Chapel in Windsor.
She is survived by her son, the new King Charles, as well as her daughter, Princess Anne, and younger sons, Prince Andrew and Prince Edward.
Philip's body will be moved from Windsor's Royal Vault to the Chapel so they can lie beside each other.
Earlier on Thursday, Buckingham Palace released a statement saying that the Queen was under medical supervision at Balmoral and that doctors were "concerned" for her health.
Her four children – Charles, Princess Anne, Prince Andrew and Prince Edward all travelled to Balmoral to be with their mother.
They were joined by her grandson Prince William and Prince Edward's wife Sophie, the Countess of Wessex.
Prince Harry joined the family at Balmoral later in the evening.
The Elizabethan era
The royal family was racked by controversies in the Queen's final years.
The Queen's grandson, Prince Harry, and his wife, Meghan, stood back from royal duties, moved to Los Angeles and accused the family of racism in an interview with US TV host Oprah Winfrey.
There was also trouble closer to home, with the Queen's son, Prince Andrew, stripped of his royal duties and military appointments as he faced sexual abuse allegations in the US, which he denied.
However, for most of her seven-decade reign, the Queen was seen as a beacon of consistency and endurance in the face of unprecedented political and societal changes.
Born on April 21, 1926, Elizabeth was the eldest daughter of Prince Albert, the Duke of York, and Lady Elizabeth Bowes-Lyon.
The pair had anticipated their lives, and the lives of Elizabeth and their youngest daughter, Margaret, would be comparatively quiet as they served in the shadow of Albert's older brother, Edward, who became King in 1936.
However, when Edward VIII unexpectedly abdicated later that year to marry American divorcee Wallis Simpson, the notoriously shy Albert was thrust into the spotlight as King George VI.
The disruption to the monarchy would be formative for Elizabeth, who would learn, at age 10, that she was heir to the throne and that, in her mother's words, "the Crown must be above all controversy".
Elizabeth's adolescence was spent training to be the future sovereign.
On September 13, 1940, the Germans bombed part of Buckingham Palace while the King, his wife and children were inside.
The then-queen refused to evacuate her daughters to Canada, unlike many wealthy British families, although they were sent to Windsor Castle outside London.
A month later, Princess Elizabeth made her first public speech, with a radio address to children of the Commonwealth.
After World War II, she married Philip of Greece (who became Prince Philip, the Duke of Edinburgh) at Westminster Abbey on November 20, 1947.
The couple's first son and heir to the throne, Charles, was born on November 14, 1948. Their second child and only daughter, Anne, was born less than two years later.
Meanwhile, Elizabeth took on extra royal duties as her father suffered serious health problems as a consequence of a long-term smoking habit.
Just months after George had a tumorous lung removed in September 1951, Elizabeth and Philip took off on a long-planned tour of Commonwealth countries.
Against medical advice, the King farewelled his 25-year-old daughter at the airport on the day of her departure.
Six days later, while in Kenya, Elizabeth was told that her father had died in his sleep, aged 56.
She acceded to the throne on February 6, 1952 and chose to keep her given name to become Queen Elizabeth II — the first woman to rule Britain since Queen Victoria died in 1901.
Her coronation at Westminster Abbey on June 2, 1953 was broadcast live on television and watched by an estimated three-quarters of the UK's population.
During her reign, she would meet almost weekly with more than a dozen different British prime ministers — a role exclusively held by men until 1979, when Margaret Thatcher took office.
What was said in those meetings was rarely publicised, as it is the sovereign's role as head of state to remain politically neutral.
It was a responsibility Elizabeth embodied for the entirety of her reign.
Publicly, she remained apolitical and reserved, refusing to comment even when her government drew fierce criticism for its actions.
But it was her own family's controversies that would prove to be the biggest threat to the Queen's crown.
Turmoil in the House of Windsor
Prince Charles's turbulent marriage to Diana Spencer brought the monarchy to its knees and precipitated the worst crisis since the abdication furore half a century earlier.
Diana's infamous 1995 Panorama interview (which BBC journalist Martin Bashir enticed her to do using fake documents) included confirmation that Charles had an extramarital affair with Camilla Parker Bowles.
The Queen was heavily criticised for her initial inaction and seeming lack of compassion when Diana died two years later in a car crash in Paris while being chased by paparazzi.
Eventually, she bowed to public pressure, visiting the floral tribute to Diana outside Buckingham Palace and comforting a mourner.
Decades later, she faced controversy again as Diana's son, Prince Harry, made his messy exit from the royal family.
Despite the turmoil, the Queen's stoic image contributed to her reputation as a stable leader, as did her relentless commitment to the job, even into old age.
She ruled for longer than any other monarch in British history, and visited nearly every Commonwealth country (with the exception of relatively recent members Cameroon and Rwanda).
Australia was one of her first and final destinations as part of her extensive royal tours.
Her debut foreign tour as Queen included a two-month stint in Australia in 1954, making her the first reigning monarch to visit the country.
She would return to Australia 15 more times. Her final visit was in October 2011 for a Commonwealth Heads of Government Meeting.
