UK Prime Minister Boris Johnson has tested positive for coronavirus.

UK Prime Minister Boris Johnson revealed Friday that he had tested positive for the coronavirus, making him the first major world leader known to have contracted the disease. Johnson was tested for COVID-19 on Thursday on the advice of England’s chief medical officer after experiencing “mild symptoms” of the virus, a spokesman for No. 10 Downing Street confirmed in a statement.

The test was carried out in No 10 by [National Health Service] staff and the result of the test was positive,” the spokesman said. “In keeping with the guidance, the Prime Minister is self-isolating in Downing Street.“He is continuing to lead the government’s response to coronavirus,” the spokesman said. Johnson’s diagnosis offers one of the most potent examples yet of how the deadly and highly transmissible coronavirus has permeated life around the world and at every level of society.