Blake Shelton has Cher wishing she never signed on to be his mentor for season 5 of The Voice, according a show insider.

Conflict and drama between the music icon and the award-winning country singer reportedly took place from the moment they started filming season 5 of the singing competiton.

"Cher wishes she never agreed to be Blake's team mentor," a set insider told National Enquirer. "She can't stand him. She's already called him a big jerk and told him how much she hated him."

Cher reportedly lost respect for Shelton because of the unprofessional attention he gave to female contestants.

"While she's a fan of Blake's musical talent, she can't seem to get over his backwoods, country cowboy ways and his constant flirting with the sexier female singers on the show."

The source also shared an eyewitness account of Cher and Shelton arguing over a political rant about President Obama.

"Cher calmly tried to warn him to leave his politics at home, especially around the younger contestants," the source revealed. "But then Blake tried to reason with her and said, 'Listen, sweetheart...' "

Shelton's attempts to end their feud were futile -- Cher reportedly screamed at him and told him she "hated" him.

"She called him a jerk and said he was 'nothing but a dumb cowboy,' " the source shared. "Blake retaliated and called her a 'typical Hollywood liberal,' and that's when she really went off, yelling, 'I hate you!'"

Despite their rumored feud, the pair will work together to try to win season 5 of The Voice.

"It's a mutual hate-hate relationship, and it'll be interesting to watch Blake and Cher try to work together. Hope­fully they won't tear each other's heads off."

Shelton hinted that he was unsure if he and Cher would get along in a recent interview. He said on Live With Kelly & Michael, "I don't know if she likes me that much."

All four of The Voice's season 5 coaches introduced their mentors on Monday, the first night of the battle rounds. Adam Levine enlisted the help of OneRepublic frontman Ryan Tedder, Christina Aguilera recruited Eddie Sheerna and CeeLo Green will work with R&B singer Miguel.

Shelton has won The Voice three times: with 16-year-old Danielle Bradbery in season 4, season 3 with his Cassadee Pope and season 2 with Jermaine Paul. Levine's contestant, Javier Colon, won season 1.

The Voice airs Mondays and Tuesdays at 8 p.m. EST.

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The Voice Season 5, The Voice 5, Blake Shelton