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Charlie Sheen announced Tuesday that he has HIV.

The 50-year actor told NBC “Today” show host Matt Lauer that he was diagnosed about four years ago but he’s not sure how he contracted the virus that causes AIDS.

“It started with what I thought was a series of crushing headaches,” he said. “I thought I had a brain tumor. I thought it was over,” he said, adding, “It’s a hard three letters to absorb. It’s a turning point in one’s life.”

Sheen said he made the announcement to cease extortion efforts.

“I have to put a stop to this onslaught, this barrage of attacks and of sub-truths and very harmful and mercurial stories that are about me, that threaten the health of so many others that couldn’t be further from the truth,” he told Lauer.

When asked what untrue report he had heard that hurt him the most, Sheen said that he knew he had the virus and “was intentionally spreading it,” which not the case, he noted.

At one point Lauer read Sheen supportive messages from fans weighing in on social media. Sheen’s response? “I’m going to ride this wave of support.”

Going forward Sheen said he would do what he can to raise awareness and help others.

The National Enquirer said it had done “an exhaustive 18-month investigation” into the life of Sheen, revealing the news this week.

Sheen was married to Brooke Mueller from 2008-2011, Denise Richards from 2002-2006 and Donna Peele from 1995-1996. The former “Two and a Half Men” star has had a long dating history, having been linked to porn stars and models, along with such high-profile actresses as Winona Ryder, Robin Wright and Kelly Preston.

In October 2014, Sheen and his fiancee, adult film star Brett Rossi, ended their eight-month engagemement.

“She’s a terrific gal — but we’ve mutually decided to go our separate ways and not spend the rest of our lives together,” he said in a statement.

Sheen has largely kept a lower-profile this year. The actor, who starred on TV in “Anger Management” and “Two and a Half Men,” made an appearance earlier this year on “The Goldbergs,” reprising his role from “Ferris Bueller’s Day Off.”

Sheen has had a history of substance abuse and famously made headlines in 2011 amid what appeared to be a public meltdown, during which he popularized his catchphrase “Winning!” Around that time, he parted ways with his long-running role on CBS’ “Two and a Half Men.”