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(CNN) -- When "Evel Dick" Donato left "Big Brother 13" during filming, he cited only "personal reasons" for his decision. He's now revealing the reason for his exit: He is HIV positive.

The winner of "Big Brother 8" shared his revelation on an episode of the VH1 reality series "Couples Therapy" set to air Wednesday. Donato and his girlfriend, Stephanie Rogness-Fischer, are cast members on the show, and in a clip he is seen discussing wanting to come clean about his diagnosis -- which she is adamantly against doing.

"Stephanie does not want to talk about it, and if it's brought up with her she will probably leave," he tells the show's therapist, Jenn Berman. "There (were) a million rumors of why I left ... but nobody ever knew and nobody ever found out."

CNN first became aware of Donato's status via Twitter.

Donato exited "Big Brother 13" after six days. He told People magazine that the show's producers first alerted him to his diagnosis.

"They told me that something was wrong with my blood test," he said. "They had done two HIV tests. One had come back positive and the other had come back negative."

He said he immediately left the show and went to the house of his mother, the first person he told. Donato said he is not gay or an intravenous drug user, "but at this point, it doesn't matter. We create a stigma around the disease that makes it hard for people to publicly say they have it."

Donato is on medication that he will have to take for the rest of his life and said he is coming forward to help others come out of the shadows. He says he's fully aware of his reputation as a reality-show villain but grateful for the platform.

"And I decided that it was time to just publicly say what I'm dealing with," he said. "On one hand, I'm doing this for myself: I don't want to hide anymore. On the other hand, I hope it will remind viewers to get tested, practice safe sex, all those things we know in the back of our minds but maybe don't do."