Oprah's secret is half-sister Bunny, whom she has never met and with whom she will be reunited

Last week Oprah Winfrey revealed that on Monday's show (Jan. 24), she would be sharing with her audience a big family secret that she says "literally shook me to my core." Now we know what that secret is.

According to Robert Feder's Chicago Tribune blog, the secret is that Kitty Kelley, Oprah's unauthorized biographer, uncovered a secret half-sister who was given up for adoption before Oprah was born.

Oprah's mother, Venita, gave birth to a daughter, Bunny, who she "gave away shortly after she was born because she couldn't afford to take care of her." Bunny, who is now a grandmother, and Oprah will be reunited on Monday's show. The pair had their very first meeting off-camera.

Will you be tuning in for what Oprah calls "the miracle of all miracles ... This time, I'm the one being reunited. Only a handful of people in my life know about this. I've been keeping a family secret for months, and you're going to hear it straight from me."