X Factor judges spoke at the Television Critics Association press tour on Monday (July 23), with Cowell discussing his chemistry with Lovato and Spears.
"[Britney is] a really, really good judge. Demi is a brat, but there's something very likeable about her as well," Cowell quipped.
He added facetiously of choosing Lovato for the panel: "[We needed] somebody a bit younger, because I'm in my 30s."
Spears also revealed that she became a fan of The X Factor on her last tour, but it was her make-up artist who actually convinced her to join the show.
"Actually, my make-up artist was the make-up artist for Simon… We just all met up and it made sense. I adore Simon and it was something I really wanted to do," she explained.
Cowell recently commented that he's been "fascinated" in watching Spears judge The X Factor during auditions.
"She's not on the show to be Britney Spears on a TV show… She's actually there to prove to the world there's more to her, and she's got the ability to do this job really well. She's taken the role really seriously," he said.
The X Factor USA's second season will debut this September on Fox.
Watch Britney Spears discuss The X Factor in a recent interview below: