Queen Elizabeth II, Britain's longest-serving monarch, died on Thursday.
Elizabeth-II died after 70 years of reign in Scotland. She was 96-years-old.
Earlier, Queen Elizabeth II iwas under medical supervision at her Balmoral Castle residence in Scotland after doctors became concerned for her health, Buckingham Palace had said.
Her son and heir, Prince Charles, his wife Camilla - Duchess of Cornwall, and grandson Prince William travelled to Balmoral to be with her, according to their Clarence House and Kensington Palace offices. The 96-year-old monarch is said to be "comfortable" at Balmoral, where she has been for her summer break.
"Following further evaluation this morning, the Queen's doctors are concerned for Her Majesty's health and have recommended she remain under medical supervision,” the Buckingham Palace statement said.
"The Queen remains comfortable and at Balmoral," it said.
The 96-year-old monarch has been suffering from age-related mobility issues and has cut down her travels, including appointing new Prime Minister Liz Truss in Scotland earlier this week.
“The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime,” Truss tweeted.
“My thoughts – and the thoughts of people across our United Kingdom – are with Her Majesty The Queen and her family at this time,” she said.
Meanwhile, House of Commons Speaker Sir Lindsay Hoyle interrupted a debate on energy bills in Parliament to update MPs about the Queen's health.
He cut short a speech to say: "I know I speak on behalf of the entire House when I say that we send our best wishes to Her Majesty the Queen and that she and the royal family are in our thoughts and prayers at this moment.
"If there is anything else, we will update the House accordingly."
The Leader of the Opposition, Labour Leader Keir Starmer, tweeted: “Along with the rest of the country, I am deeply worried by the news from Buckingham Palace this afternoon.
“My thoughts are with Her Majesty The Queen and her family at this time, and I join everyone across the United Kingdom in hoping for her recovery.”
According to reports, the Queen had been due to hold the Privy Council meeting of senior government advisers virtually on Wednesday evening but it was decided it would be rearranged.
(With PTI inputs)
