The Prince of Wales is 71, putting him in one of the high-risk categories, according to government guidance.
The Duchess of Cornwall, 72, has also been tested but does not have the virus, PA Media reports. The couple are currently self-isolating at home in Scotland.
A Clarence House spokesperson said: “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.”
Charles’s last public engagement was on March 12, but he did have a number of private meetings with Highgrove and Duchy individuals, all of whom have been made aware.
A source said his doctor’s most conservative estimate was that the prince was contagious on March 13, which is after he last visited the Queen.
Clarence House said it was “not possible to ascertain” how the prince contracted the virus “owing to the high number of engagements he carried out in his public role during recent weeks”.
Earlier this month Prince Charles attended an event with Monaco’s ruler, Prince Albert II, who later tested positive for coronavirus.
A small number of people living and working at Birkhall are remaining at the residence and self-isolating and the prince and the duchess remained in good spirits. Prince Charles was up and about and not bedridden.
Medical advice is that it is unlikely to escalate into a more serious case.
Charles has spoken to his sons Prince William and Prince Harry, as well as the Queen.
A Buckingham Palace spokeswoman said: “Her Majesty The Queen remains in good health.
“The Queen last saw The Prince of Wales briefly after the investiture on the morning of March 12 and is following all the appropriate advice with regard to her welfare.”
This article originally appeared on HuffPost.