The Queen has sparked new health concerns as she has been forced to cancel a planned video meeting with ministers.
It comes just one day after the 96-year-old Royal appointed Liz Truss as the UK's new Prime Minister.
In a statement, Buckingham Palace said: "After a full day yesterday, Her Majesty has this afternoon accepted doctors’ advice to rest.
"This means that the Privy Council meeting that had been due to take place this evening will be rearranged."
"The Queen is under medical supervision at Balmoral after doctors became concerned for her health."
Both Prince Charles and Prince William are heading to Balmoral now to visit her.
Buckingham Palace has given no further details about the Queen's health but said the latest advice from her doctors did not require the need to visit a hospital.
It comes after the Queen had to axe her planned welcome at her Scottish home earlier this month.
The monarch was due attend the annual ceremony in Scotland tomorrow on August 9, but the day was cancelled and replaced with a "small, private event" instead.
Usually, the Queen greets the public at the gates to her beloved castle to mark the start of her yearly holiday.
With the exception of the Covid pandemic, Her Majesty has not missed the public welcoming in decades.
It's not the first time that the Queen has pulled out of a public event in recent months and the continued cancellations have sparked more fears about her health.
Here's everything we know about the Queen's current health.
Queen latest health updates
In recent months the Queen has been forced to cancel a number of appearances due to what the Palace has said is "episodic mobility problems ".
In February 2022 it was revealed that the monarch had contracted Covid-19 and that she was experiencing "mild cold-like symptoms".
The Queen cancelled a number of work commitments while she recovered from Covid, but since then she has continued to reduce her in-person appearances due to mobility concerns.
In May, she pulled out of the State Opening of Parliament, which she had only ever missed twice during her reign, both times when she was pregnant.
A statement from the Palace said: "The Queen continues to experience episodic mobility problems, and in consultation with her doctors has reluctantly decided that she will not attend the State Opening of Parliament."
In June, Her Majesty also had to pull out from attending the Platinum Jubilee Service of Thanksgiving at the last minute after the Palace confirmed she "did experience some discomfort” at the Jubilee parade.
She also missed out on attending the Epsom Derby after it was reported that the she found the Jubilee celebrations "very tiring".
Her Majesty has also not hosted any of her annual garden parties this summer, with other royals filling in for her.
She then missed the Commonwealth Games, which have been held in Birmingham this year.
Most recently, her appointment with Liz Truss also sparked some concerns when people noticed her 'blue hand'.
Members of the public shared their concern from the meeting, with one writing on Twitter: “What is going on with the queen’s hands? All blue and purple?”
Another added: “The queen seems to be suffering from circulation issues.. her hands are blue.”
Buckingham Palace did not address the concerns from the meeting.
Regarding her cancelling the minister's video meeting today, Royal expert Royal expert Robert Jobson voiced his concern on the Australian morning show Sunrise, saying: "I think something is afoot.
"It's not very clear and they're not going to give running commentary of the Queen but the very fact they used the wording 'doctor's advice' is slightly worrying.
"In all the other stories before it was simply advice and that the Queen would listen to people's advice but the word doctor's alarms me.
"The fact that it's a virtual meeting too. She's been very good at keeping in touch with people through the pandemic using computers and Zoom meetings.
"The very fact she can't even do that does suggest it's not quite right."
Earlier this year, it was reported that the Queen had had a wheelchair lift fitted at Craigowan Lodge on the Balmoral estate, so that she could spend more time there.
