Andy Cohen 'Regrets' Asking Oprah Winfrey If She's Ever Been Intimate With a Woman: 'Couldn't I Leave It Alone?'

Andy Cohen has one major regret about his big interview with Oprah Winfrey .

Looking back on the 15 years he's been hosting Watch What Happens Live , the television star, 56, opened up about the one question he wished he'd never asked when chatting with the media legend, 70.

"This was a huge moment for me and for the show," he said of welcoming Winfrey on his late-night series. "I'm such a fan of Oprah."

However, things took a bit of a turn when Cohen questioned The Color Purple actress if she'd ever "taken a dip in the lady pond" before. "That's probably one of my few regrets," the Bravo boss admitted.

"It meant so much to me that Oprah Winfrey did the show," he added. "It's gone brilliantly, and I turn around and ask her if she's every had s-- with a woman. I mean, couldn't I leave it alone?"

Although Winfrey was cool was it, her best friend later told Cohen how confused she was by the question. " Gayle King told me later that week that Oprah didn't know what I meant by 'the lady pond,'" the executive producer said. "I thought I explained it pretty well there, but listen, I was so grateful that Oprah did the show and I still am. That remains, I think, my favorite episode."

Cohen also opened up about one of his other favorite guests, Patti LuPone , and how her appearance ruffled some feathers with Madonna after the Tony winner called the pop star a "movie killer" for her work in the Evita film. "I mean, Patti LuPone has no F's to give so she is the perfect clubhouse guest," he noted of the Gypsy star. "She's been here many times."

"This clip got me in a lot of trouble with Madonna, who called me a 'troublemaking queen' from the stage of her Celebration Tour. [She] said, 'You need to stop talking crap about me on your show,'" Cohen explained. "Now the truth is, it wasn't me talking c--- about her. It was people like Patti LuPone ....who I also love, by the way."

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"The secret to the success of Watch What Happens Live, I think, is spontaneity, authenticity, fun, humor, me going there and people never knowing what's going to happen," Cohen added. "People let their guard down here. It's also live, we're on at night, we serve alcohol."

Entertainment Tonight conducted the interview with Cohen.