"She's known Charlie was HIV-positive for a number of years," a source tells PEOPLE of Sheen's ex.
"He was infected after they divorced, and they haven't been intimate since," adds the source of the news (which was originally reported by Access Hollywood). "Neither she nor their daughters [Sam, 11, and Lola, 9] are HIV-positive."
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Richards, now 44, filed for divorced from Sheen in 2005 after nearly three years of marriage. Their split was declared legally official in 2006.
Speaking to PEOPLE correspondent Matthew Cole Weiss last week for his podcast Allegedly with Theo Von & Matthew Cole Weiss (which preceded Sheen's latest revelation), Richards responded to a social media question about how she has approached discussing her ex-husband: "I really wanted to protect our daughters and him, you know – what he wanted to reveal, that's his choice. There's so many different circumstances surrounding that one question ... I'm not quite sure which one [to address]."
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As Sheen prepares for Tuesday's TV appearance, Hollywood publicist and crisis manager Howard Bragman, who has never dealt with Sheen directly, told PEOPLE that "the interview could open up a lot of sympathy for him, but he has to be concerned about a fear of litigation from former sexual partners. You don't take that lightly."
Bragman says he was informed by people close to Sheen that the star "is getting treatment, and a lot of people in his life know about it."
"It's been going on for quite awhile. He's not necessarily comfortable talking about it. It was very hard to get up the courage for him to talk about it."
When reached by PEOPLE, Sheen's longtime publicist Jeff Ballard said they are no longer working together. "We had a disagreement how to handle a situation and we parted ways. We have had a 35-year friendship and I love him. I wish him nothing but the best."
To learn more about living with HIV/AIDS today and to contribute in the fight against the diseases, visit amfAR.org.