Of course he should be tested - his last public engagement (less than two weeks ago) was an Investiture for approx 60 people - he may have been infected by someone at the event. Or perhaps someone who had travelled from Australia:
12 March 2020 Buckingham Palace
The Prince of Wales, on behalf of The Queen, held an Investiture at Buckingham Palace this morning.
12 March 2020 Clarence House
The Prince of Wales, President, The Prince's Trust, this afternoon held a Meeting.
His Royal Highness afterwards received Mr. Mark Carney (Governor of the Bank of England).
The Prince of Wales this evening attended a Dinner in aid of the Australian Bushfire Appeal, Mansion House, Walbrook, London EC4.
Busy day on the 11 March as well: Clarence House
The Prince of Wales, President, The Prince's Trust Group, this morning received Mr. Anthony Pratt (Founding and Cornerstone Patron, The Prince's Trust Australia).
His Royal Highness afterwards held a Sustainable Markets Meeting.
The Prince of Wales, Royal Founding Patron, University of Cambridge Institute for Sustainability Leadership, this afternoon held a Meeting.
His Royal Highness, President, later attended The Prince's Trust Awards at the London Palladium, Argyll Street, London W1, and was received by Her Majesty's Lord-Lieutenant of Greater London (Sir Kenneth Olisa).
The Duchess of Cornwall, Honorary Member, the Jockey Club, today attended the Cheltenham Festival at Cheltenham Racecourse and was received by Her Majesty's Lord-Lieutenant of Gloucestershire (Mr. Edward Gillespie).