Oprah Winfrey shocked viewers yesterday by revealing she has a half-sister named Patricia — who she just learned about last fall.

Winfrey, 56, and Patricia, who’s nine years younger, share the same mother, Vernita Lee — who never revealed to anyone that she’d given up a baby (Patricia) for adoption in 1963.

Oprah and Patricia met for the cameras on yesterday’s “Oprah,” and Patricia sat for a long interview with her half-sister.

“Imagine my shock just a few months ago, at the end of October, when I found out I have another sister living just 90 minutes away,” Winfrey said.

“I was 9 years old at the time of [Patricia’s birth], living with my father in Nashville, Tenn.,” Winfrey said. “I had no idea my mother was even pregnant.”

Winfrey had another half-sister, also named Patricia (Lloyd), who died in 2003 at the age of 43 after battling drug addiction. Winfrey’s half-brother, Jeffrey Lee, died in 1989 from AIDS.

All four siblings had different fathers.

“For the most part, my life has been an open book . . . And I thought nothing could surprise me anymore — but let me tell you, I was wrong,” Winfrey said.

Patricia, a single mother of two, said she’s known since 2007 that Winfrey is her half-sister — but it took her several years to get in touch with the talk show queen and convince her it was true. (It’s since been confirmed by DNA testing.)

Patricia first tried years ago to (unsuccessfully) search for her birth mother, who’d given her up for adoption in Milwaukee.

Her two grown children then urged her to try again — but she was told that her birth mother didn’t want to meet her.

Then, on that very same day, she saw a news report on local TV about Vernita Lee, who talked about her two children, Patricia and Jeffrey, and how they had died.

That information was very similar to what Patricia was told by the adoption agency, and she traced herself to Vernita Lee — and then to Winfrey.

“It feels to me like you are [her late half-sister] Pat on her very best day,” Winfrey told Patricia on yesterday’s show. “You are what she wanted to be without the drugs.”

Author Kitty Kelley, who wrote “Oprah: A Biography,” which was published last year, says she didn’t know about the other Patricia introduced on yesterday’s show.

“I did not know this info at the time I wrote my hardback . . . nor did I know it for the paperback edition of ‘Oprah,’ out this week,” she said in an e-mail to The Post.

“But the paperback contains more ‘family secrets.’ “