Dominick Brascia told the National Enquirer in a widely circulated report that 19-year-old Sheen had sex with 13-year-old Corey Haim on the set of their 1986 movie "Lucas."
Haim was a former child star who died in 2010 of pneumonia at the age of 38 after years of substance abuse.
"Haim told me he had sex with Sheen when they filmed 'Lucas,'" said Brascia, who was Haim's lifelong friend.
"He told me they smoked pot and had sex. He said they had anal sex. Haim said after it happened Sheen became very cold and rejected him. When Corey wanted to fool around again, Charlie was not interested."
"Charlie Sheen categorically denies these allegations," Sheen's representative told The Hollywood Reporter Wednesday.
The report came as another of Haim's friends -- actor Corey Feldman -- has publicly claimed he and Haim were sexually abused by men in the entertainment industry when they were children.
Feldman recently filed a complaint with the Los Angeles Police Department against the men he has said hurt him.
He also is attempting to raise via crowd-sourcing the $10 million he said he needs for legal and security fees, as well as to make a documentary about pedophilia in Hollywood.
Sheen, now 52, was fired in 2011 from his popular CBS sitcom "Two and Half Men" due to his substance abuse issues and erratic behavior.
He went on to star in the FX comedy series "Anger Management" and, in 2015, he announced he was diagnosed as HIV positive four years prior.
Deadline.com reported Tambor's transgender, former assistant Van Barnes has alleged the 73-year-old actor behaved inappropriately with her.
Amazon -- which streams Tambor's celebrated show "Transparent" -- said it is investigating the matter.
"I am aware that a former disgruntled assistant of mine has made a private [Facebook] post implying that I had acted in an improper manner toward her," Tambor told Deadline Wednesday.
"I adamantly and vehemently reject and deny any and all implication and allegation that I have ever engaged in any improper behavior toward this person or any other person I have ever worked with. I am appalled and distressed by this baseless allegation."
"Anything that would diminish the level of respect, safety and inclusion so fundamental to our workplace is completely antithetical to our principles. We are cooperating with the investigation into this matter," "Transparent" creator Jill Soloway said in a statement to Variety.
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