(AP) -- Former "Two and a Half Men" star Charlie Sheen has the HIV virus.

In an interview Tuesday on NBC's "Today," the 50-year-old Sheen said he tested positive for the virus that causes AIDS.

But when asked by "Today" co-host Matt Lauer if he had transmitted the disease to others, he declared, "Impossible. Impossible."

He said he was diagnosed about four years ago. He said one reason for going public with his condition was to put a stop to shakedowns from prostitutes and others who threatened to out him. He said he had paid "enough to bring it into the millions" -- perhaps as much as $10 million -- to buy their silence and now was seeking to "put a stop to this barrage of attacks and sub-truths."

He said one prostitute took a photo of the HIV-related drugs in his medicine cabinet and threatened to sell it to the tabloids.

"Are you still paying these people?" Lauer asked him.

"Not after today I'm not," Sheen said.

With his public pronouncement he said he hoped to reduce the stigma still felt by some diagnosed with HIV.

"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, for kicking the door open.'"

The disclosure was only the latest chapter in Sheen's headline-seizing behavior. In recent years, drug and alcohol use led to his being kicked off CBS' "Two and a Half Men" in 2011 after an explosive meltdown that included calling the show's producer "a contaminated little maggot."

His escapades also included the revelation that he spent more than $50,000 as a client of "Hollywood Madam" Heidi Fleiss' prostitution ring.

"Two and a Half Men" debuted in 2003 and starred Sheen as womanizing bachelor Charlie Harper. It made Sheen one of TV's highest-paid actors and at its peak was TV's most-watched sitcom. It ended its run earlier this year, after Ashton Kutcher stepped in for the fired Sheen.

In 2012, Sheen returned to TV in "Anger Management," an FX sitcom adapted from the movie of the same name.

Sheen has been wed three times, the first time to model Donna Peele in the 1990s.

He and actress Denise Richards were married from 2002-2006 and have two daughters. Sheen and real estate investor Brooke Mueller wed in 2008 and divorced in 2011; they have two sons. Sheen said he had informed her of his diagnosis.

___

AP writer Lynn Elber contributed to this report.