"I'm not even kind of a lesbian," the talk-show queen, 56, tells Barbara Walters in an upcoming interview on ABC. "And the reason why [the rumor] irritates me is because it means that somebody must think I'm lying. That's number one. Number two ... why would you want to hide it? That is not the way I run my life."
The rumors have focused on Winfrey's friend Gayle King. But Winfrey says that relationship is extremely close in a whole different way.
"She is ... the mother I never had. She is ... the sister everybody would want. She is the friend that everybody deserves. I don't know a better person. I don't know a better person," Winfrey says while choking up.
"It's making me cry because I'm thinking about ... how much ... I probably have never told her that. Tissue, please. I now need tissue. I've never told her that."
The occasion for the interview, airing Thursday at 9 p.m. ET on ABC, is the end of Winfrey's syndicated show next May and the beginning of her new cable network – OWN, The Oprah Winfrey Network.
On that subject, Winfrey admits to having been afraid of how daunting the new project is. "I was very scared," she says. "I would wake up in the middle of the night literally like clutching my chest, like, 'What have I done? What have I done?' "