Prince Charles, the 71-year-old heir to the British throne, has tested positive for coronavirus but is in good health, Clarence House has said.

Key points: It remains unclear how the Prince caught the virus

It remains unclear how the Prince caught the virus Camilla Parker Bowles, the Duchess of Cornwall, returned a negative result

Camilla Parker Bowles, the Duchess of Cornwall, returned a negative result Buckingham Palace has confirmed Queen Elizabeth II remains in good health

The Prince, who is the eldest son of Queen Elizabeth II, is believed to be displaying mild symptoms but has continued working from his Birkhall residence in Scotland.

His wife, Camilla Parker Bowles the Duchess of Cornwall, was also tested and returned a negative result.

"The tests were carried out by the National Health Service in Aberdeenshire where they met the criteria for testing," the statement from Clarence House read.

The Duchess of Cornwall did not test positive to coronavirus but remains in self-isolation with Prince Charles. ( Pool Photo via AP: Aaron Chown )

"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 the recent weeks."

A royal source told Reuters the earliest the Prince would have been infectious was March 13.

The Royal couple went to Highgrove House, Prince Charles' residence in west England, on March 13 and then travelled to their Birkhall residence on the Balmoral estate in Scotland on Sunday.

They have been self-isolating in Scotland since the positive test result.

Those involved in private meetings with the Prince have also been made aware of his condition.

The Prince has also spoken to his sons, Princes William and Harry.

Queen Elizabeth II 'remains in good health'

The Queen (left) is the United Kingdom's longest-reigning monarch. ( Reuters: Russell Cheyne )

A statement from Buckingham Palace has confirmed that Queen Elizabeth II, 93, "remains in good health".

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

The Queen left London for Windsor Castle on March 19.

She is with her 98-year-old husband, Prince Philip, the Duke of Edinburgh.

Prince Charles joins Prince Albert of Monaco with diagnosis

The news comes in the wake of Prince Albert of Monaco testing positive for COVID-19, becoming the first monarch to be diagnosed with the disease.

He and Prince Charles attended the same charity event in London on March 10.

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Prince Charles's last public engagement was an Australian bushfire relief dinner on March 12, with George Brandis, Australian High Commissioner to the UK, in attendance.

An Australia House spokesman told the ABC Mr Brandis had no symptoms and was following UK Government advice.

"Mr Brandis, like all staff at Australia House, is following the guidance published by the UK Government," the spokesman said.

"All of us at the Australian High Commission wish His Royal Highness a speedy recovery."

Prime Minister Boris Johnson also wished Prince Charles a speedy recovery and was due to hold his weekly audience with the Queen by telephone, Mr Johnson's spokesman said. His wishes were echoed by a spokesperson for the Trump administration.

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