L.A. Reid, Demi Lovato, Britney Spears and Simon Cowell on the set of “The X Factor.” (Ray Mickshaw/Fox)

NBC’s decision to add a third night of “The Voice” blind auditions next week at the exact same time Fox launches its reboot of “X Factor” is “mean-spirited,” Simon Cowell whined Thursday — like a chick who’s just discovered her frenemy Madison has scheduled her unicorn-themed birthday party on the EXACT same day she’s scheduled her princess-themed birthday party.

“I hope and I pray that it backfires on them,” Cowell told The Reporters Who Cover Television on a conference call Thursday afternoon, including The Post’s Emily Yahr.

“They don’t want people to see this first episode,” he said of NBC’s scheduling change announcement, just days before “The Voice” is set to debut its first fall season.

“I am kind of pissed off about it, because there was kind of a gentleman’s agreement,” he said, which we think is the first time someone has accused network suits of being gentlemen.

“But you have to rely that the viewers will make the right selection. I think three nights in a row is too much,” he concluded happily.

On the other hand, he wasn’t going to forecast which show would come out the winner in the head-to-head combat.

“I’ve learned:Don’t make any predictions,” Cowell said pointedly, throwing our minds, such as they were, back one year, to when when he’d boasted that his new “The X Factor” would land 20 million viewers. Which it never did in its first season. Which, in turn, caused him to dump Paula Abdul and Nicole Scherzinger as fellow judge/mentors, and replace them with Britney Spears and Demi Lovato — the latter of whom joined Cowell on the conference call.

“I think the girls do a great job,” he said of the new judge/mentors.

“The contestants look great, the show looks different from anything else we’ve ever made before — and I think this is the reason why NBC decided to put ‘The Voice’ up against us. It is a spoiling tactic,” he said, not ready to let go of his complaint against the network that airs his other show, “America’s Got Talent.”

At some point, he stopped for breath, and Demi Lovato got in a word edgewise, saying of NBC’s scheduling move, “I think the whole situation is a little unfair and I don’t know why they would do that.”

“But ultimately, it’s about finding a superstar and giving people the chance to win a huge prize of $5 million,” Lovato continued. We’d wondered how long it would take them to bring up that $5 million prize.

“That’s all that I really care about,” she insisted.

“I’m honored to be on the panel — let alone on a TV show — especially having a job in this economy,” she said.