'The Voice' Wanted Celine Dion Full Time

Celine Dion's guest appearance on "The Voice" has been a long time coming, but it's not going down exactly how the show originally wanted it ... TMZ has learned.

Our 'Voice' sources tell us Celine's been approached to do the gig a few times, but politely declined given the demanding schedule of her Las Vegas residency. We're told she was first approached to be a full-time judge in the rotating chair like Adam Levine or Blake Shelton, but since it's a several month-long commitment, Celine declined.

She's accepted an offer to coach since it only requires two days of filming. As for getting in the rotating chair in the future, NBC knows they'd have to cough up a lot of dough since she banks so much off her Vegas shows, so it's probably not going to happen. Regardless, "The Voice" will go on ...