Buckingham Palace today took the rare step to announce the Queen has been placed under medical supervision after doctor's voiced concern for Her Majesty's health.
After 70 years of her reign the move has raised fears that the Queen's recent troubles with health and mobility might be worsening.
Prince Charles, Camilla, Prince Harry and Meghan Markle and Prince William have all rushed to Balmoral to be by her side while other members of the royal family have been informed.
However, even as the family descends on the monarch's Scottish holiday home, Kate Middleton has not.
But there's a good reason for this; the Duchess of Cambridge has remained in Windsor because today is the first day of school for Prince George, Princess Charlotte and Prince Louis.
As such, she has remained home while William made the trip north to Balmoral where, in a statement, the Queen was said to be remaining comfortable.
Why Kate Middleton isn't flying to see Queen at Balmoral
In a statement Kensington Palace said: "The Duchess of Cambridge has remained in Windsor as Prince George, Princess Charlotte and Prince Louis are on their first full day at their new school."
The 96-year-old monarch celebrated her Platinum Jubilee this year but there have been longstanding concerns over her health and mobility.
And with her husband Prince Philip sadly passing away last year on April 9 2021, and her son Prince Charles taking on more of her duties and reportedly making plans for a "slimmed down" monarchy, thoughts have turned to her eventual passing.
Follow the latest updates on the Queen's health today in our live blog
This morning, in market contrast to this afternoon's news, cheery and upbeat pictures of the Cambridges taking their children to school were released.
The three Cambridge children, George, aged nine, Charlotte, seven and Louis, four, have enrolled in the prestigious Lambrook school in Berkshire - which costs more than £53,000 every year - after the family recently moved out of London to Windsor.
The school's headmaster Jonathan Perry met the Cambridge clan at the entrance, stepping forward to greet them.
The Duchess, who appeared to know Mr Perry and his wife well after the long process of choosing the right school, greeted them like an old friend, saying: "Nice to see you, Mr Perry!"
What should have been an exciting day for the family has taken a sad turn with news of the Queen's health.
The news follows months of growing concern about the 96-year-old’s health over a period where she has pulled out of several official and private engagements.
The initial statement read: "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 Queen remains comfortable and at Balmoral."
It comes only days after the Queen met with Liz Truss to officially appoint her as the new Prime Minister.
In light of the news, Ms Truss sent a message on Twitter and said: “The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime. My thoughts - and the thoughts of people across our United Kingdom - are with Her Majesty The Queen and her family at this time."
The nation’s longest-reigning monarch has ongoing mobility issues. She looked bright but frail and used a walking stick during Tuesday’s historic audience with Ms Truss.
This followed a visit from ousted prime minister Boris Johnson as he tendered his resignation.
The news also followed speculation on social media after politicians were seen looking shocked and passing notes in the House of Commons earlier today.
Interrupting proceedings speaker Lindsay Hoyle said to MPs: "We send our best wishes to HM the Queen and that she and the Royal Family are in our thoughts and prayers at this moment."
Labour leader Sir Keir Starmer said he is “deeply worried” by the news from Buckingham Palace and added that he is hoping for the Queen’s recovery.
He 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.”
The Archbishop of Canterbury has also said the “prayers of the nation” are with the Queen.
“My prayers, and the prayers of people across the (Church of England) and the nation, are with Her Majesty The Queen today,” Justin Welby tweeted.
“May God’s presence strengthen and comfort Her Majesty, her family, and those who are caring for her at Balmoral.”
The monarch had been due to hold a Privy Council meeting virtually yesterday but it was postponed.
