Donald Trump—self-avowed “ratings machine” though he might be—has finally gone too far for Fox News Chairman Roger Ailes.

The Republican presidential front-runner, who has spent the past day tweeting and re-tweeting nasty insults about Fox News star Megyn Kelly, owes her an apology, Ailes demanded in an extraordinary broadside against the reality-show billionaire, issued on Tuesday afternoon.

“Donald Trump’s surprise and unprovoked attack on Megyn Kelly during her show last night is as unacceptable as it is disturbing,” Ailes said about Trump, who has been a frequent interview guest on Fox & Friends, The O’Reilly Factor, Hannity, and other Fox News programs since the Republican presidential debate that Fox News broadcast on August 6 at which Kelly asked him a tough question about his history of calling women “fat pigs, dogs, slobs and disgusting animals.”

Trump immediately fired back in a statement.

“I totally disagree with the FOX statement. I do not think Megyn Kelly is a quality journalist. I think her questioning of me, despite all of the polls saying I won the debate, was very unfair. Hopefully in the future I will be proven wrong and she will be able to elevate her standards to a level of professionalism that a network such as FOX deserves.”

Ailes issued his statement a little more than 12 hours after Trump’s angry tweet storm.

“Megyn Kelly represents the very best of American journalism and all of us at FOX News Channel reject the crude and irresponsible attempts to suggest otherwise,” Ailes continued, referring to a raging series of Trump tweets in which the candidate claimed Kelly was “off her game” on her first show after a 10-day vacation, and retweeted a crass assertion that the former Washington litigator is a “bimbo.”

Ailes, who scheduled The Kelly File at the all-important 9 p.m. prime-time slot, went on:

“I could not be more proud of Megyn for her professionalism and class in the face of all of Mr. Trump’s verbal assaults. Her questioning of Mr. Trump at the debate was tough but fair, and I fully support her as she continues to ask the probing and challenging questions that all presidential candidates may find difficult to answer.

“Donald Trump rarely apologizes, although in this case, he should. We have never been deterred by politicians or anyone else attacking us for doing our job, much less allowed ourselves to be bullied by anyone and we’re certainly not going to start now. All of our journalists will continue to report in the fair and balanced way that has made FOX News Channel the number one news network in the industry.”

Ailes's verbal howitzer against the front-running Republican—a highly unusual deployment for any news organization, let alone one that has been the GOP establishment and home of conservative viewers—comes after what seemed a coordinated defense of Kelly by at least 10 other Fox News personalities today on Twitter and on air.

According to CNN’s Brian Stelter, the pro-Kelly comments included Fox & Friends co-host Brian Kilmeade opining on Tuesday’s show that Trump is “totally out of control”; The Five co-host Dana Perino tweeting, “The intelligence, class & grace of Megyn Kelly shined last night after her week's vacation with her family"; anchor Bret Baier, Kelly’s co-moderator at the debate, tweeting that Trump "has made his feelings clear. But THIS needs to stop;" and Sean Hannity tweeting to Trump, "Leave @Megynkelly Alone."

So far, there has been no word on whether Trump will be welcome on Fox News if he continues his attacks and refuses to apologize.