Osbourne told her fellow co-hosts that the affair happened just as she arrived to the U.S. as a "not very dateable" 25-year-old in 1978.
She disclosed that this happened during her pre-Ozzy Osbourne dating days.
"Remember, at 25, I had met my husband but we weren't together. We were just friends," said the daytime host.
Since she was single, a friend suggested that Osbourne come down to the club where she was employed. Once there, she spotted Leno whom her friend described as "very nice, very funny." Her pal also happened to have his phone number so they decided to prank call him.
Osbourne described the phone call: "He liked my voice and I kept calling. I said I had the wrong number but I kept talking with my English accent."
Eventually, the two met in person and the mother-of-three disclosed that Leno "actually came to my house and met me and we had a little fling."
The affair didn't last very long because Leno introduce her to the "real love of his life" and the trio became friends.
"The fling was more of a fling for me and not fling enough for him because a couple of months later he brought around the real love of his life for me to meet, and she was lovely and they took me to Fatburger and showed me around town," she said.
Of course, Osbourne kept the identity of her suitor secret from her co-hosts and the audience until the end of the story. The one tricky thing about the whole tale is whether Leno was dating his now-wife Mavis at the same time he had the fling with the CBS star.
The audience didn't seem to care as they cheered and applauded over the revelation.
Co-host Julie Chen said, "Whoa, whoa, whoa, I don't know if Sharon is getting the standing ovation or if Jay Leno is getting the standing ovation."
The Big Brother host also had the chutzpah to ask Osbourne if she slept with the late-night personality.
Osbourne wisely replied with a laugh, "It was so long ago I can't remember! One cannot remember that long ago."
Leno wound up marrying Mavis in 1980 while Sharon married Ozzy in 1982.
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