At a July press conference, Cowell said he's long been intrigued by Spears.
"I didn't know her as a person, and I thought it would be interesting to have her on one of these shows so you see another side of her, and she's a really, really good judge," Cowell said. "Demi is a brat. But there's something really likeable about her as well. And I think the show, because it has such a young audience, it needed someone younger, because I'm in my 30s."
"Yes, add about 100," Lovato said, showing off what may be the show's secret weapon: the chemistry between Cowell and Lovato.
Fox didn't make a full screener of tonight's episode available but in clips, Lovato and Cowell seem to have a lot of fun together.
When members of an auditioning boy band tell Lovato she's "the bomb," she replies, "I think your'e pretty cute too."
Simon, perhaps trying to avoid another Paula Abdul fiasco, says, "No, no, no! Barrier!"
"Thanks, dad," Lovato replies.
"Pleasure, brat," Simon snaps back.
In another clip, Lovato says of Simon, "He's old and impatient and whatever."
While viewers may tune in to see how much of a train wreck Spears turns out to be, perhaps it will turn out that they stick around for the Demi and Simon show.