She was the family secret that Lady O called "one of the greatest surprises" of her life.

But on Monday's Oprah Winfrey Show, Patricia, the media mogul's half-sister, stepped forward in a very public way.

During the show, Winfrey revealed that she learned she had a sister last October, saying the discovery "left me speechless."

She was 9-years-old and living with her father in Tennessee when her mother, Vernita Lee, became pregnant with a daughter, Patricia, who was given up for adoption. Born in 1963 in Milwaukee, Patricia would later live in a series of foster homes until the age of 7. She was then adopted, but said her childhood was "difficult."

Tracing her roots took years of perseverance but Patricia finally discovered her mother – and her half-sister.

"I received this big old package of information in the mail," Patricia said during Monday's interview. "And it has all of my birth information in it. I was like, 'Oh my god. I have a family.' "