Actor Charlie Sheen is seen through a window as he sits on the set of the NBC Today show prior to being interviewed by host Matt Lauer in the Manhattan borough of New York City, November 17, 2015.[Photo/Agencies]

NEW YORK - Former "Two and A Half Men" television star Charlie Sheen said on Tuesday he is HIV positive.

Sheen, 50, told NBC's "Today" show he was diagnosed about four years ago and said the reason he disclosed the information was because he was being blackmailed.

"I am here to admit that I am in fact HIV positive," Sheen said, saying he was "not entirely sure" how he acquired the virus.

"It's a hard three letters to absorb," he added.

Sheen, who is three times divorced, played the womanizing bachelor Charlie Harper on top-rated US comedy series "Two and A Half Men" for eight years before being fired in 2011 for bad behavior that included cocaine-fueled partying with porn stars and a conviction for assaulting his ex-wife.

At the time, he was the highest paid actor on U.S, television with a reported annual salary of some $1.8 million.

Asked whether he had transmitted HIV to anyone since his diagnosis, Sheen said on Tuesday, "Impossible."

The actor said he had "always led with condoms and honesty when it came to my condition."

Sheen said one of the reasons he disclosed the news about his health was to stop others from extorting him. He would not disclose how many people he was paying for their silence, but said the payments reached into the millions of dollars to people he once considered in his inner circle.

"What people forget is this is money, money they are taking from my children," Sheen said, referring to his 5 kids and one grandchild.

"I thought they could be helpful. Instead, my trust turned into their treason," Sheen said, adding he will no longer pay those people.

"I think I released myself from this prison today," he said.

After being fired from "Two and A Half Men," Sheen set up home with a number of porn stars he called "goddesses" and boasted on YouTube of having "tiger blood" in his veins.

Sheen, the son of "West Wing" TV actor Martin Sheen, also starred in the cable TV comedy "Anger Management," which was closely based on his life, from 2012-2014.

He has five children from his marriages to model Donna Peele, actresses Denise Richards and Brooke Mueller, and other relationships.