Idris Elba caught coronavirus from another celebrity.
The 47-year-old actor revealed on Monday (March 16) he had tested positive for the virus - which can cause body aches, a high fever and a dry cough - but Idris has now revealed why he was tested without experiencing any symptoms.
Taking to his Instagram account on Thursday (March 19), he explained: "I was told that someone I had been in contact with had tested positive.
"I'm on location, about to start filming and the news breaks that this person, who is also in the public eye, had tested positive.
"My job made me test immediately. I had to test because it meant putting a lot of people at risk who I was working with on a new film. We were really lucky to get tested really quickly. I quarantined myself and have been here ever since."
Idris didn't name the celebrity who passed on the virus, but he did confirm he was exposed at the start of the month.
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He said: "The early testing is the way we need to approach this.
"It's hard to say when I contracted the disease. I was exposed to it from March 4th."
Since his diagnosis, the Luther star has been self-isolating at home with his wife Sabrina.
Idris continued: "I wasn't showing any symptoms - but I am very glad I made that decision to get tested. I have been out of contact with everyone since."
The London-born actor also urged his social media followers to remain calm and to not increase panic by spreading fake news.
He said: "Please stop sending conspiracy theory nonsense about black people not being able to get coronavirus. It's dumb and very dangerous."
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