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Get ready for another huge Oprah Moment.

Oprah Winfrey plans to stage a family reunion on her eponymous daytime show this Monday -- and drop a bombshell while she's at it.

"I thought I'd seen it all," Winfrey, 56, teased in a promotional clip for the show that debuted late Friday. "But this, my friends, is the miracle of all miracles."

The star added tantalizingly: "I was given some news that literally shook me to my core. This time, I'm the one being reunited. I was keeping a family secret for months, and on Monday you're going to hear it straight from me."

No further details were provided about the major revelation. Winfrey, of course, has been frank about her difficult past: She was born into poverty, sexually abused at a young age and lost a baby at age 14.