Charles previously contracted the coronavirus in March 2020, during the first wave of the pandemic. Officials said he had mild Covid-19 symptoms then, and Charles said later that Charles and Camilla isolated in Scotland at the time.
Britain's Press Association news agency reported that Charles recently met with his mother, Queen Elizabeth II, but the monarch was not displaying any symptoms.
The queen, 95, marked her Platinum Jubilee on Sunday by expressing her wish for Camilla to be known as Queen Consort when Charles becomes king.
Camilla carried on with her engagements as scheduled, visiting a sexual assault referral center in London.
Spain's King Felipe VI, 54, and Denmark's Queen Margrethe II, 81, also tested positive for the coronavirus this week.
- AP