Gwen Stefani on 'The Voice' -- Taking Christina Aguilera's Seat as Judge

Gwen Stefani's gonna make good money off Christina Aguilera getting knocked up -- TMZ has learned Gwen has signed on to be a judge on "The Voice."

Multiple sources connected to the show tell us ... No Doubt's lead singer will be on Season 7 ... which starts taping in June.

Producers started looking for new blood in February after Christina announced she was pregnant. Makes sense ... she'd be 8 or 9 months along by the time Season 8's battle rounds began.

We're told NBC wanted Christina to stay during her pregnancy but she's having a difficult time already and ultimately bowed out.

Gwen's deal is for one season right now, and we're told Christina has already signed on to rotate back into her spinning chair for Season 8.