Meghan Trainor will fill the remaining seat on FOX's new singing competition "The Four" ... TMZ has learned.
Production sources say FOX execs were noodling on 3 female candidates for the final spot -- Trainor, Fergie and BeBe Rexha. She'll be joined by some superstar talent on the panel ... DJ Khaled, Diddy and music honcho Charlie Walk.
The show -- which has an emphasis on hip-hop -- features 4 contestants who will face challengers throughout the course of the season who try and knock them off their spots. The winner will start a music career mentored by "The Four" judges.
We're told Meghan will actually tour with the winner and help launch the singer's career.
The show is set to premiere in January.