Oprah Winfrey promised to stage a family reunion and reveal a family secret on her show on Monday, which airs at 4 p.m. EST.

Over the past 25 years, The Oprah Winfrey Show has united lots of families, said the Monday show's promotional trailer.

On Monday, however, the secret involves her own family.

I was given some news that literally shook me to my core, said Oprah.  Only a handful of people in my life know about this.

She said it's the miracle of miracles and she's been keeping this secret for months.

So what will she reveal on Monday?

For starters, we know it's a reunion with someone, as indicated by the promotional trailer.

Also, it isn't likely to be something negative because she called it miracle of miracles.

In fact, it's probably going to be a heart-warming story, given the nature of Oprah's shows.

Fans (and critics) have been speculating on Twitter.  Of the serious guesses, a long lost child is the most common.   Another rumor is the identity of her biological father.

Click here to view the promotional trailer for the show.