The Queen and Prince Philip face weeks in self-isolation at Windsor Castle with a skeleton staff after Prince Charles revealed he has tested positive for coronavirus.
The Prince of Wales, 71, has a "mild" form of the illness and is on the Balmoral estate with his wife Camilla, the Duchess of Cornwall, who has tested negative and is without any symptoms of the virus, which has killed 435 and infected 8200 more in the UK so far.
A royal source said Charles' doctor's most conservative estimate was that the prince was contagious on March 13 - 24 hours after "briefly" meeting his 93-year-old mother the Queen.
A Buckingham Palace spokesman has said: "Her Majesty remains in good health. The Queen is following all the appropriate advice with regard to her welfare."
It is not known if the monarch has been tested for coronavirus but she is now in "virtual" self-isolation and not even close family members can see her.
Her weekly meeting with the Prime Minister is being done by phone, rather than in person at Buckingham Palace, where a worker tested positive for coronavirus while the Queen was still in residence last week.
The Queen and the Duke of Edinburgh, who was helicoptered to Windsor from Sandringham last Thursday, are being looked after by her two favourite staff, who are part of a skeleton team of just eight.
The rest of her 100-plus workers have all been told to go home to protect both the head of state and themselves.
Charles tested positive yesterday - a fortnight after meeting coronavirus-stricken Prince Albert of Monaco, who tested positive five days ago, after he sat opposite the Prince of Wales at a WaterAid event in London on March 10.
A Clarence House spokesman said: "The Prince of Wales has tested positive for coronavirus. He has been displaying mild symptoms but otherwise remains in good health and has been working from home throughout the last few days as usual.
"The Duchess of Cornwall has also been tested but does not have the virus. In accordance with government and medical advice, the Prince and the Duchess are now self-isolating at home in Scotland The tests were carried out by the NHS in Aberdeenshire where they met the criteria required for testing."
A royal spokesperson insisted there was no way to know how Charles had contracted the highly contagious illness because he has met with so many people in recent weeks.
The representative added: "The tests were carried out by the NHS in Aberdeenshire, where they met the criteria required for testing.
"It is not possible to ascertain from whom the Prince caught the virus owing to the high number of engagements he carried out in his public role during recent weeks."
But questions will be raised over whether it came from Albert and if the heir to the throne has spread it himself.
In the past two weeks, Charles has given a speech at a dinner in aid of the Australian bushfires and at his own Prince's Trust award in London.
It was revealed at the weekend the couple had relocated to Balmoral for the foreseeable future due to the pandemic.
The virus had already caused Charles and Camilla to postpone a planned official tour of Bosnia, Herzegovina, Cyprus, and Jordan.
The World Health Organisation says the incubation period for Covid-19 can be as long as 14 days.
CHARLES' MOVEMENTS
There is some anger that Prince Charles was tested by the NHS in Aberdeenshire when medical staff across the UK are being denied them.
British media have plotted the prince's movements over the past 16 days. He attended at least six public engagements meeting hundreds of people including a string of Britain's biggest stars at his annual Prince's Trust awards at the Royal Albert Hall two weeks ago - the start of the coronavirus 14-day incubation period.
The Prince of Wales was last at Buckingham Palace on March 12 to carry out investiture on behalf of the Queen, who he also "briefly" met.
His coronavirus diagnosis will raise fears for the health of elderly royals including his mother and Philip, 98, who are together at Windsor Castle, especially because of the high death rate among the elderly.
Charles is understood not to have seen his father for many weeks, possibly during the Megxit crisis talks at Sandringham, where his 98-year-old father was based until he flew by helicopter to Windsor last Thursday.
William and Kate are at Anmer Hall in Norfolk, while Harry and Meghan are back in Canada, after both couples saw Charles at the Commonwealth service at Westminster Abbey on March 9.
At the service no members of the royal family shook hands, with the Prince greeting people with Namastes and the Duke of Sussex elbow bumping Craig David.
Two days later, on March 11, he also met with a string of celebrities at the Prince's Trust Awards 2020 in London, attended by Ant and Dec, Philip Schofield, Fearne Cotton, Pierce Brosnan, Richard E Grant, Rolling Stones star Ronnie Wood, X Factor star Fleur East, Dina Asher-Smith and Craig David.
Arriving at the Prince's Trust awards a fortnight ago, Charles twice extended his hand to greet people before withdrawing it at the last minute in mock horror and greeting them with a bow and the Hindi greeting Namaste.
Turning to Dame Martina Milburn, the Trust's chief executive, the prince said: "It's just so hard to remember not to."
On the evening of March 12, after investitures at Buckingham Palace, Charles was with the Lord Mayor of the City of London and the High Commissioner for Australia at a Mansion House dinner in London, his last known public engagement.
But he did have a number of private meetings with Highgrove and Duchy individuals, all of whom have been made aware of his illness.
He flew to Birkhall, his Balmoral home, with Camilla on March 22 - around the time he started feeling unwell. A small number of people living and working at Birkhall are remaining at the residence and self-isolating.
Charles had been displaying "mild symptoms" over the weekend before being tested on Monday.