Today is the day...Oprah reveals her shocking "family secret."

In a promo for her show, she hypes, "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. I thought I'd seen it all. But this, my friends, is the miracle of all miracles."

Show promos are prompting speculation that she'll either reconnect with a long-lost sibling or biological father.