According to a report by TMZ, Charlie Sheen has known for a year that he's HIV positive but kept it under wraps but it all unraveled when some former partners threatened him with lawsuits. TMZ reports below...
As we reported, Charlie will appear on "Today" and reveal he's HIV positive. We're told he's known about his status for more than a year and he kept a lid on the information. We're told things changed when Charlie confided in several friends he thought were confidants ... it turned out they weren't, and spread the word he was HIV positive.
That led to several of Charlie's former partners contacting him and threatening a lawsuit because they were unaware of his status when they had interaction with him. Our sources say Charlie settled several of the cases and, in return for money, got confidentiality agreements.

We're told one of the settlements occurred late last month.

We also know when people go to Charlie's house they are almost always required to sign confidentiality agreements which require anyone who might make a claim to do so in arbitration and not through the courts ... which thereby keeps things private.