The Queen was in direct contact with the Prince of Wales before he tested positive for Covid, a Palace source has said.
It is understood Her Majesty, 95, is not displaying any symptoms and the situation will continue to be monitored.
Clarence House said that Charles, 73, tested positive during a routine test this morning.
It has not been confirmed when exactly the prince met with the Queen but a royal source told the BBC they met two days ago.
Charles held an investiture on Tuesday at Windsor Castle, where the monarch is currently staying.
Her majesty is understood to be fully vaccinated so will not need to self isolate, unless she tests positive.
But she will be advised to take rapid lateral flow tests, one a day for seven days.
Palace sources have refused to confirm whether or not she has tested negative.
The Queen was out and about on public duties on Saturday, the eve of her Jubilee, meeting charity workers at Sandringham House.
Four days ago, the nation’s longest reigning monarch reached her historic Platinum Jubilee of 70 years on the throne.
This morning The Prince of Wales has tested positive for COVID-19 and is now self-isolating.
— The Prince of Wales and The Duchess of Cornwall (@ClarenceHouse) February 10, 2022
HRH is deeply disappointed not to be able to attend today's events in Winchester and will look to reschedule his visit as soon as possible.
The prince, who first fell ill with Covid-19 in 2020, was said to be “deeply disappointed” to have to pull out of engagements in Winchester after a positive test on Thursday.
A message on his official Twitter page read: “This morning the Prince of Wales has tested positive for Covid-19 and is now self-isolating.
“HRH is deeply disappointed not to be able to attend today’s events in Winchester and will look to reschedule his visit as soon as possible.”
Clarence House confirmed the 73-year-old prince is triple vaccinated, but has not given any other update on his condition.
He will now need to self-isolate under current rules for 10 full days, but he could be free after five days if he tests negative on day five and day six.
