Multiple sources tell us ABC was desperate to sign a name before the Upfronts last week, when honchos announced she was the lead judge. As one source put it, "Katy had all the leverage. If ABC ended up announcing the show without a judge, they'd be screwed."

TMZ broke a story way back in 2012 that 'A.I.' was trying to get Katy as a judge but she rejected the network's $20 mil offer.

As we reported, ABC tried to get Kelly Clarkson but at the last minute she jumped ship and went to NBC's "The Voice." NBC also snagged Jennifer Hudson.

We're also told ABC is "on the verge" of signing the deal with Ryan Seacrest to host the show. Sources connected with the first run of 'Idol' tell us Ryan was making $15 mil a season at his high point. We're told Jennifer Lopez was also raking in $15 mil a season. So Katy blew them both away.