The Prince of Wales, 71, has had a “high number of engagements” in recent weeks and it is “not possible to ascertain” where he caught the virus, his spokesman said.

Charles – who has since spoken to his mum the Queen and sons William in Norfolk and Harry in Canada – is the first Royal Family member to be diagnosed with Covid-19, and he falls within one of the highest risk categories given his age.

Clarence House said he “otherwise remains in good health” and has been working from home over the last few days despite catching the potentially deadly illness.

Camilla, the Duchess of Cornwall, has tested negative for coronavirus and is self-isolating at Birkhall in Scotland along with her husband, although they are apart from each other at the residence.

Charles last saw the Queen after an investiture ceremony at Buckingham Palace on March 12, and she was in “good health” at Windsor Castle on Wednesday, a spokesperson said.

The 93-year-old monarch and her two corgis left her central London residence for Windsor last Thursday, a week earlier than usual for Easter, and is following social distancing guidelines with Prince Philip, 98.

Charles’ positive test, meanwhile, was carried out by the NHS in Aberdeenshire in Scotland, where he had been at Highgrove before going to Birkhall on Sunday.

Six staff members are self-isolating as well.

A Clarence House spokesman 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.

“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.

“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.”

The prince travelled to Birkhall on Sunday and he was tested on Monday.

The source said the prince and the duchess remained in good spirits, and 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 the Duke of Cambridge and the Duke of Sussex, as well as the Queen.

There were fears for the Queen when Clarence House announced that Charles had tested positive.

A Buckingham Palace spokeswoman said: “Her Majesty The Queen remains in good health.

How to self-isolate

For those concerned they have coronavirus in the UK, Public Health England has issued advice about how to self-isolate.

1. Stay at home: Don’t leave your house except when you need to seek medical care. Ask for help buying groceries or have them delivered.

2. Stay away from your housemates: Stick in a well-ventilated room away from others, with the door closed. Use a separate bathroom and wear a facemask when it is shared areas.

3. Call ahead before visiting the doctors so they can take extra precautionary measures.

4. Cover your coughs and sneezes: Make sure to cover your nose and mouth and to throw away disposable tissues in a plastic waste bag.

5. Wash your hands regularly: This should be done often and thoroughly with soap and water, for at least 20 seconds, rinse and dry thoroughly.

6. Avoid sharing household items: You should not share dishes, drinking glasses, cups, eating utensils, towels, bedding or other items with other people in your home when you have used them. After using these items, wash them thoroughly with soap and water.

7. Do not have visitors in your home.

8. Keep away from your pets if possible.

9. Keep your clothes clean: Do laundry on the highest temperature possible and clean all surfaces around the washing machine.

10. Monitor your symptoms: Seek prompt medical attention if your illness is worsening, for example, if you have difficulty breathing, or if the person you are caring for symptoms are worsening.

“The Queen last saw The Prince of Wales briefly after the investiture on the morning of 12th March and is following all the appropriate advice with regard to her welfare.”

Charles’ recent engagements include the March 12 investiture ceremony at Buckingham Palace, where he offered a namaste gesture instead of a handshake, and a dinner that night at Mansion House in London in aid of the bushfire relief effort in Australia.

At the Prince’s Trust Awards in London on March 11, he offered a namaste gesture as he greeted actors Michael Ward and Ashley Walters.

Prince Albert of Monaco tested positive for coronavirus nine days after attending the same event as Charles.

The pair were in the same room for a WaterAid event at Kings Place in London on March 10, when Charles addressed the audience.

Prince Albert was the first head of state and reigning monarch to reveal they had been diagnosed with Covid-19.

Monaco said he was doing fine despite the diagnosis.