The Hollywood Reporter said the six-episode musical event will be an origins story for the characters the actors played in the 2017 live-action blockbuster.
Deadline said the project was written by Gad and Once Upon a Time creators Eddy Kitsis and Adam Horowitz.
Composer Alan Menken -- who created the music for Beauty and the Beast, as well as the 1991 animated movie musical on which it was based -- is in talks to return for the limited series.
Kitsis and Horowitz are no strangers to the Beauty and the Beast universe.
The fairy tale was woven into Once Upon a Time, with Robert Carlyle's Rumpelstiltskin playing the Beast and Emilie de Ravin as Belle.