Queen Elizabeth II has died at age 96 at Balmoral Castle, United Kingdom, the Buckingham Palace announced Thursday.
"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,” Buckingham Palace said in a statement on Thursday.
The Queen is succeeded by her eldest son and heir, former Prince of Wales, as King Charles III. He will lead the country in mourning as the new King and head of state for 14 Commonwealth realms.
"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.
"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," Charles said in a statement.
According to the BBC report, all the Queen's children travelled to Balmoral, near Aberdeen, after doctors placed the Queen under medical supervision. While her grandson, Prince William, was also there, his brother, Prince Harry, is on his way, he said.
The Queen came to the throne in 1952 and reigned for 70 years, making her UK's longest-reigning Monarch.
Elizabeth was born in Mayfair, London on April 21, 1926, as the first child of the Duke and Duchess of York.
Meanwhile, many leaders took to Twitter to condole the demise of The Queen.
Expressing grief over the demise of the Queen, UK Prime Minister Liz Truss said Queen Elizabeth II leaves a great legacy.
"Queen Elizabeth II was the rock on which modern Britain was built. Our country had grown and flourished under her reign. 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, God save the King," the UK prime minister tweeted.
Liz Truss is the third female premier of the UK. She was formally appointed as Britain's new Prime Minister by Queen Elizabeth II on Tuesday.
President of France Emmanuel Macron recalled The Queen as a friend of France.
"Her Majesty Queen Elizabeth II embodied the British nation’s continuity and unity for over 70 years. I remember her as a friend of France, a kind-hearted queen who has left a lasting impression on her country and her century," President Macron tweeted.
"Our thoughts are with the royal family and all those who mourn Queen Elizabeth II in the UK and worldwide. Once called Elizabeth the Steadfast, she never failed to show us the importance of lasting values in a modern world with her service and commitment," European Union (EU) president Charles Michel tweeted.
Prime Minister Narendra Modi tweeted, "Her Majesty Queen Elizabeth II will be remembered as a stalwart of our times. She provided inspiring leadership to her nation and people. She personified dignity and decency in public life. Pained by her demise. My thoughts are with her family and people of the UK in this sad hour".
PM Modi also recalled memorable meetings with Queen Elizabeth II during his UK visits in 2015 and 2018.
"I had memorable meetings with Her Majesty Queen Elizabeth II during my UK visits in 2015 and 2018. I will never forget her warmth and kindness. During one of the meetings she showed me the handkerchief Mahatma Gandhi gifted her on her wedding. I will always cherish that gesture," PM Modi tweeted.
Paying homage to The Queen, UN Secretary-General Antonio Guterres tweeted, "I am deeply saddened at the passing of Her Majesty Queen Elizabeth II, admired worldwide for her leadership & devotion. She was a good friend to the @UN & a reassuring presence through decades of change. Her unwavering, lifelong dedication will be long remembered".