“You’re a hack.”

From the moment Bill O’Reilly debuted his Fox News show in 1996, he has stuck to a one-note strategy when dealing with critics: attack. The difference now for O’Reilly is that the critic is one of Fox’s highest-profile pundits. Last Thursday, Fox contributor George Will published a Washington Post column headlined “Bill O’Reilly Slanders Ronald Reagan.” The scathing piece slammed O’Reilly’s best-selling Killing Reagan as a “lurid” book full of “unsubstantiated assertions.” Not surprisingly, Will’s column made O’Reilly go ballistic. On his show Friday, O’Reilly called Will a “hack” and a “liar.” Will responded with one of the more memorable lines to be uttered on Fox News, telling O’Reilly: “You’re something of an expert on willfully misleading people.”

What makes the exchange so fascinating is that O’Reilly pulled the curtain back and discussed Fox’s internal workings on air, something that never happens at Roger Ailes’s secretive network. “Fox News hard news chief Mike Clemente, who you know, told us that you told him that you would call me before the column was published,” O’Reilly said on-camera. Will disputed that Clemente issued a directive. “It would not be the first time you got something wrong,” Will told O’Reilly.

Inside Fox, the O’Reilly-Will feud is being closely studied by executives because it is part of a larger power struggle that’s taking place at the highest reaches of the organization. On opposing sides of the fault line are Clemente, who oversees news (where Will works), and executive vice-president Bill Shine, who oversees prime-time shows (where O’Reilly works). Clemente and Shine are vying to replace Ailes and are such bitter rivals that they barely speak, numerous Fox employees say. In August 2014, the rivalry intensified when Ailes put Shine in charge of the Fox Business Network. “This is some Game of Thrones shit,” one insider told me. The relationship is so bad that Clemente is not involved at all in preparing for the upcoming GOP debate on Fox Business.

Shine’s loyalists tell me that Clemente did not confer with Shine about Will’s anti-O’Reilly column before it was published. Furthermore, they’re furious at Clemente for not stopping Will from embarrassing Fox’s highest-rated host in the pages of the Post. They reminded me that it was Clemente who recruited Will to Fox from ABC in 2013. One source also explained that Will received a special contributor contract with Fox that grants him editorial independence for his column (other contributors are barred from writing about Fox without permission). “He doesn’t have to check with Fox,” the source said.

Clemente did not comment, but his camp is firing back off the record. “Almost everyone is on team George,” one said. “Everyone is snickering and thinks it’s a riot.” Another told me that O’Reilly’s Killing series is considered something of a joke inside the network. “He certainly doesn’t research his books,” one executive said.

Where Ailes stands remains unclear. In the past he’s been critical of O’Reilly’s book-writing ventures. In my biography of Ailes, I reported Ailes told colleagues that O’Reilly is “a book salesman with a TV show.” Fox News has not commented on the mess. “Roger is probably in the men’s room hoping this whole thing blows over,” one insider told me today. That might be wishful thinking. The rumor at Fox is that Will is preparing to write another O’Reilly column. Will did not respond to requests for comment.

Irena Briganti, a Fox News spokesperson, did not respond to requests for comment.