Big O-nouncement on Oprah

11/20/2009 11:38 AM PST

Big O-nouncement on Oprah

UPDATE: Oprah knows a thing or two about sweeps -- and is saving her big announcement for the end of the show.

is about to personally announce that she's ending her reign as maybe the most successful person ever to host a show on TV. And you can see it all go down on TMZ.

BTW, as we first reported, Oprah insiders are telling us one of the reasons behind the timing is that Oprah is angling to get ABC to slide "The Dr. Oz Show" into her time slot. "Oz" becomes a free agent at exactly the same time Oprah will go off the air.

We're also told other talk shows are angling to get the time period, which is primo real estate in TV land.