Jewel, Alanis Morissette, Kenny "Babyface" Edmonds, Robin Thicke and Ne-Yo have also agreed to provide their expertise on the series, which returns with a special premiere following Super Bowl XLVI on February 5. (The season will begin in its regular time slot on Monday, February 6 from 8 to 10 p.m.)
Thicke and Morissette will mentor for members of Adam Levine's team, while Clarkson and Lambert will offer their services to Blake Shelton's team. Singers coached by Cee Lo Green will have Edmonds and Ne-Yo dispensing their wisdom, and Christina Aguilera's team will have Jewel and Richie on their side.

The guests will offer their services during the "battle rounds" of the series, which pits two artists from each team against each other to sing a duet.
The timing of Clarkson's inclusion on the series is particularly interesting. The "Breakaway" singer recently gained headlines (and probably a few enemies) with her endorsement of GOP presidential candidate Ron Paul. Clarkson, who's gearing up to tour in support of her most recent album "Stronger," will also serve as musical guest on the year's first new episode of NBC's "Saturday Night Live" this weekend.
"These renowned musicians will bring their unique and recognizable musical styles to the teams. They are well-respected singers whose invaluable experience will be a tremendous asset to Christina Aguilera, Cee Lo Green, Adam Levine and Blake Shelton's artists," Paul Telegdy, NBC's president, late night and alternative programming, said of the upcoming guests.
Reba McEntire, Sia, Adam Blackstone and Monica served as guest mentors on the show's inaugural season.
Javier Colon, from Adam Levine's team, won the first season of the series, which was adapted from the Dutch TV program "The Voice of Holland."

source: yahoo