CHRISTINA AGUILERA and CEE LO GREEN will NOT return to "The Voice" for Season Four, which will premiere next spring.  Christina is releasing a new album and going out on tour . . . while Cee Lo is working on two albums, and is developing an NBC sitcom based on his life.

Unlike "American Idol" and "X Factor", "The Voice" has immediately named their replacements . . . and they're BIG NAMES.

 SHAKIRA will take Christina's seat, and USHER will take Cee Lo's chair.

ADAM LEVINE and BLAKE SHELTON will be back for the spring season . . . although they could take some time off the following season.  For now, Christina and Cee Lo are expected to return for Season Five next fall.

--By the way, "Us" magazine says both MARIAH CAREY and NICKI MINAJ were "in talks" to do "The Voice" before they landed gigs on "American Idol".  They were going to be seat-warmers for Christina and Cee Lo next season.