American actor Charlie Sheen, as well known for his off-screen debauchery with drugs, alcohol and prostitutes as his on-screen work, has disclosed that 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 yesterday, saying he was “not entirely sure” how he acquired the virus.

“It’s a hard three letters to absorb,” he added.

Sheen said that when he first started feeling sick, he had terrible migraines and so much sweating at night that it drenched his bed. It was so bad he thought he had brain tumour and was close to death.

The actor, who is three times divorced, played the womanising bachelor Charlie Harper on top-rated US comedy series Two And A Half Men for eight years before being fired in 2011 for bad behaviour that included cocaine-fuelled partying with porn stars and a conviction for assaulting his former wife.

At the time, he was the highest paid actor on US television with a reported salary of some US$1.8 million (S$2.6 million) per episode. (See correction note)

Asked whether he had transmitted HIV to anyone since his diagnosis, Sheen said “impossible”.

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