Inside Christina Aguilera, Adam Levine's Nasty Feud

USMagazine, Wednesday, May 9, 2012, 6:45am (PDT)

Christina Aguilera may have apologized to The Voice contestant Tony Lucca after Tuesday's finale, but that doesn't mean her feud with Lucca's coach, Adam Levine, has tempered.

Levine, 33, showed off a "Team Xtina" shirt on Monday's episode as a peace offering after Aguilera, 31, declared Lucca's "99 Problems" performance "derogatory," but a source close to Aguilera tells the new issue of Us Weekly the singer is "livid" over Levine's behavior.

PHOTOS: Nasty celeb feuds

"You could cut the tension with a knife," says the source of the atmosphere during Monday's taping in Los Angeles.

Making no secret of her distaste for her former Mickey Mouse Club costar Lucca, Aguilera worried fans would think his song was about her. Aguilera especially objected to the use of the word 'bitch' in the original lyrics, which Lucca ended up mouthing on the live broadcast.

VIDEO: Does Tony still want to duet with Christina?

For his part, coach Levine insisted he and Lucca collaborated when choosing to cover the Jay-Z hip-hop hit, but it was the Maroon 5 singer himself who pushed Lucca to perform, as a way to stick it to Aguilera. When producers told Lucca he couldn't say 'bitch' during rehearsals, Levine stormed off set.

VIDEO: Adam taunts Christina after she slams Tony

"Adam also talks a ton of s--t about Christina and makes fun of her behind her back," a show insider explains.

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This article originally appeared on Usmagazine.com: Inside Christina Aguilera, Adam Levine's Nasty Feud