Charlie Sheen admitted in a "Today" show interview with Matt Laeur on Tuesday that he is HIV positive.

"It's a hard three letters to absorb," the former "Two and a Half Men" star told the host. "It's a turning point in one's life."

The 50-year-old "Wall Street" actor and son of legendary actor Martin Sheen added he decided to go public about his condition in hopes of ending a smear campaign and repeated extortion plots aimed against him.

"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 said.

While claiming he has previously shared the news with those he felt could handle it, he admitted that he has also paid out "upwards of $10 million" to keep the illness a secret.

"What people forget is that it's money taken from my children," he added of all the "shakedowns" he has been forced to endure. "I trusted them and they were deep in my inner circle, and I thought they could be helpful. My trust turned to their treason."

Sheen told Laeur he was first diagnosed with the disease about four years ago, but doesn't know how he contracted the virus. Initially, he said he started to experience "crushing headaches" and thought he was suffering from a brain tumor.

He later insisted it was "impossible" that he knowingly transmitted the virus to anyone else, though he admitted to having unprotected sex withat least two other people since the diagnosis. Sheen added he now takes four pills every day.

Meanwhile, the actor's doctor insisted his primary battle is not overcoming the disease itself, but making sure he doesn't lapse into past substance abuse problems or depression related to his diagnosis.

"We're petrified about Charlie," physician Robert Huizenga said. "We're so, so anxious that if he was overly depressed, if he was abusing substance, he would forget these pills and that's been an incredible worry."

Sheen also claimed he shared news of his diagnosis with ex-wives Denise Richards and Brooke Mueller soon after he received it, and he added he also recently confided in his eldest daughter.

Sheen rose to prominence as one of Hollywood's best-known actors through his work in such films as "Wall Street" and "Red Dawn." More recently he became the highest paid actor on TV through his starring role in "Two and a Half Men."