A press release by the Prince of Wales and the Duchess of Cornwall's official website confirms that Prince Charles met all the criteria of testing.
As per the press release, the Prince of Wales was tested positive for Coronavirus as he was displaying mild symptoms. The Prince of Wales and the Duchess of Cornwall were self-isolating at home in Scotland and the tests were carried out by the NHS in Aberdeenshire where they had met the criteria required for the coronavirus testing.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.