Credit: Todd Williamson/

As promised, Oprah Winfrey spilled the beans on her shocking family secret during her show, broadcast in Chicago Monday morning.

The big reveal: Winfrey, 56, discovered a half-sister she never knew she had. Named Patricia, the sibling was given up for adoption as a child in 1963, and now lives in Milwaukee, Wisc.

The talk show guru learned about the long-lost relative in November, and they met up in November.

Patricia had long been searching for the identity of the mother who gave her up for adoption; in 2007, she discovered that world-famous Winfrey was her half-sister.

As for Oprah, she says she was 9 years old and living with her father, Vernon, when her mother gave birth to Patricia and gave her up. Winfrey didn't even know about her mom's pregnancy, she says.

"I thought I'd seen it all," Winfrey teased about the discovery on Friday. "But this, my friends, is the miracle of all miracles."

She added that the news "literally shook me to my core." The mogul has been frank on her show about her difficult past: She was born into poverty, sexually abused at a young age and lost a baby at age 14.