Charlie Sheen Charlie Sheen

Charlie Sheen confirmed he is HIV-positive on Tuesday's Today show.

"I'm here to admit that I am in fact HIV-positive," Sheen, 50, told Matt Lauer as the interview began.

Sheen said he was diagnosed "roughly four years ago," but decided to come forward now "to put a stop to this onslaught ... of attacks and subtruths" he's been faced with in recent weeks.

The Two and a Half Men alum insists that he's been upfront with every sexual partner about his condition since his diagnosis, and has only had unprotected sex with two women since - both of whom, he claims, were "completely under the care of [his] doctor" and were aware that he was HIV-positive.

Is Charlie Sheen HIV-positive?

It's "impossible" that he would have transmitted the virus to anyone else, he notes. (His doctor, Robert Huizenga, who also appeared with him on Today, corrected this statement to note that it's "incredibly rare" that he would transmit the virus, if he was having protected sex.)

Sheen says he's been a victim of "extortion" and "betrayal" by former sexual partners who demanded money from him in exchange for their silence about his condition. One prostitute he had hired reportedly took a photo of retroviral medications in his bathroom and threatened to post the photo online, Sheen says.

When asked by Lauer to pinpoint exactly how much he had paid out over the years, Sheen said it was "enough to bring it into the millions." "What people forget is that's money they're taking from my children," he added. (Sheen has five children and one grandchild.)

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However, he says he's no longer going to be paying the women he describes as blackmailers after his Today interview. "I release myself from this prison today," he told Lauer.

Sheen said he's not sure how he contracted the virus, but his health problems started with night sweats and a "series of crushing headaches, insane migraines" about four years ago. "I thought I had a brain tumor. I thought it was over," he told Lauer.

"It's a hard three letters to absorb," he said of his diagnosis. "It's a turning point in one's life."

Lauer inquired whether Sheen's infamous meltdown in 2011, during which he gave a series of interviews about his "tiger blood" and "winning," came as a result of his diagnosis. "I wish I could blame it on that," Sheen said with a wry grin. "That was more of 'roid rage. This was on the heels of that."

Sheen says he's no longer doing drugs (minus the four medications he takes for his HIV treatment), but is still drinking. Huizenga, who described the actor as "healthy," said that Sheen's past substance abuse issues are their biggest concern about his treatment. "My biggest concern with Charlie as a patient is substance abuse and depression as a result of the disease," he told Lauer. "We're petrified about Charlie. We're so, so anxious that if he was overly depressed, if he was abusing substances, he would forget [to take] these [medications]. That's been an incredible worry."

Sheen said he hopes that by coming forward, he will inspire other HIV-positive people to overcome the stigma associated with HIV and be open about their diagnosis.

"I have a responsibility now to better myself and to help a lot of other people," he said. "And hopefully with what we're doing today, others may come forward and say, 'Thanks, Charlie. Thanks for kicking the door open.'"

What did you think of Sheen's Today show interview? Watch excerpts here: