Reilly also said not all of those in contention are "household names."
The show was forced to revamp its panel when Jennifer Lopez and Steven Tyler parted ways with the show after two seasons by what Reilly called a "mutual agreement." Reilly declined to comment on whether Randy Jackson would return to the show, but made it sound likely. Carey was considered a likely candidate to join "Idol" because Jackson is her manager.
"I'm not going to talk about the deal in regards to the judges," Reilly said of Jackson's chances of returning. "We're not confirming it. We have a very close relationship with Randy. He's a very important part of that television show. So in the next week or so we'll confirm that.
He said he also expected executive producer Nigel Lythgoe to return, even though negotiations are still underway. "That's still a negotiation that's going on. It's not a difficult one."
Lythgoe told reporters Monday that he hoped to see the judging panel change every year, something Reilly said may be a possibility.
"I think change is going to be a part of the show going forward," Reilly said. "We're 12 years old. I think we've got to keep it fresh. It's a lot of work. It's not without risk. ... We're going to keep playing with the formula."
Reilly announced Carey was joining the show at the Television Critics Association summer press tour, in an extraordinarily low-key way. In what at first felt like the setup for a joke about rampant "Idol" speculation, he said Fox had just closed a deal with "the biggest recording artist that any of these shows have ever had."
He then dialed the new judge on his cell phone.
"Hi, Mariah?" he said. "How are you? It's Kevin."
It wasn't a joke. Reilly put his phone on speaker, and Mariah Carey came on the line to address a few hundred reporters.
"I am so excited to be joining 'Idol,'" she said.
It was no coincidence that Reilly officially announced Lopez's exit on the same day Carey was announced as a new judge.
"We were waiting for the Mariah deal," Reilly told reporters. He said that Fox didn't think of her, however, as a replacement for Lopez.
Fox had held off on announcing Lopez's exit even after she said she planned to leave "Idol." It did release a statement for Tyler.
The lack of a formal Lopez announcement made it appear there might be a slight chance of bringing her back. Lythgoe fanned that spark by suggesting at another TCA panel -- barely an hour before Reilly spoke -- that he hoped Lopez might be persuaded to return.
With Reilly's comments on Lopez's exit, those hopes seem to be completely dashed.
He said the next "Idol" judge doesn't need to be "a household name" -- but said that viewers would need "something to talk about."
Reilly acknowledged the difficulty of landing new "Idol" judges in a market so glutted with singing shows. Fox's own "X Factor," hosted by former "Idol" judge Simon Cowell, recently hired Britney Spears and Demi Lovato in an attempt to pull a younger audience for its second season this fall.
"It would be nice... if we were the only ones negotiating with these people," he said.
