Britain's Queen Elizabeth II is under medical supervision at her Balmoral Castle residence in Scotland after doctors became "concerned" for her health, Buckingham Palace said on Thursday, as members of the royal family are gathering at the monarch's Scottish estate.
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.
It is very unusual for Buckingham Palace to put out a statement like this -- it is usually unwilling to provide a commentary on the monarch's medical matters, which are seen as private, the BBC reported.
The Queen's daughter, Princess Anne, was already by her side at the Scottish castle and her other children -- Prince Andrew and Prince Edward -- are also on the way.
Prince Harry and Meghan, the Duke and Duchess of Sussex who were in Britain for a charity event, also travelling to be with Harry's grandmother.
William's wife Kate, the Duchess of Cambridge, has remained in Windsor as their children -- Prince George, Princess Charlotte and Prince Louis -- started their first full day at a new school there earlier on Thursday.
The Queen 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. The last-minute cancellation of what would only have been a virtual meeting of senior ministers have heightened concerns for the Queen's health.
However, royals are keen to quash unnecessary speculation, including some reports that she may have suffered a fall.