The BBC's veteran royal expert has explained why the announcement about the Queen's health this afternoon should be taken seriously.
Buckingham Palace confirmed this afternoon (Wednesday) doctors are concerned about Queen Elizabeth's health.
The monarch is currently resting at Balmoral with senior members of the Royal Family travelling to the Scottish estate to visit her.
A statement from Buckingham Palace said: "Following further evaluation this morning The Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision."
It added that the Queen remains comfortable at Balmoral.
The Queen's immediate family members have been informed with the latest announcement escalating fears for the 96-year-old monarch's health.
The head of state pulled out of a virtual Privy Council on Wednesday after doctors ordered her to rest.
BBC Royal Correspondent Nicholas Witchell meanwhile has told why the statement is so serious.
He said: "I think this is clearly a very significant moment. For all of the reasons that we have been saying over the last hour or so.
"The fact that the palace, which doesn’t usually comment on the state of her health or the progression of her wellbeing.
"The fact that it is saying that the doctors are concerned, though they say she remains comfortable at Balmoral.
"The fact that immediate family members are gathering at Balmoral. Prince Charles who is of course staying at the Balmoral estate at Birkhall, he’s traveling over and has been regularly going to see his mother while he’s been staying there.
"The fact that I think says the most is the fact that Prince William is flying up to Balmoral from the south. So I think, all in all, this is a very sombre moment.
"I think as politicians are saying there is a profound concern. I think it was Nicola Sturgeon who used that phrase and I think that is absolutely right and other politicians echoing that sentiment.
"Hoping for the best but, let's be completely candid now, braced for the worst."
In a later update on the BBC's rolling news coverage, he described a "deep concern among members of the Royal Family.
Mr Witchell also referred to rumours the Queen had suffered from cancers.
He said: "I think we must assume that there are reasons for concern. There has been this gradual deterioration in the Queen's health.
"Over the past months, there has been no sharp and sudden deterioration. But I think clearly over the past 24 to 48 hours, the doctors have become rather more concerned.
"It comes back to this issue that we were just discussing a moment ago as to whether it is merely this mobility issue, or whether there is and has been something else and you know, I think we can be candid, there have been rumours of cancers but no, of course, confirmation and one wouldn't expect that to be because there is an insistence by members of the Royal Family which is reflected by royal officials, that these matters are private. It doesn't matter who you are, you are still entitled to private patient confidentiality."
