Not even Fox News knew that conservative commentator Sean Hannity was a client of President Donald Trump's personal attorney Michael Cohen until it was revealed in court Monday — and media ethics experts across the political spectrum are calling foul.

Hannity is the host of a primetime opinion show on Fox News, as well as a conservative talk radio show. He regularly discusses the president's legal affairs and has often defended Cohen amid his mounting legal conflicts, particularly in the wake of an April 9 raid on the lawyer's office and residence.

Hannity, an outspoken Trump supporter who has a warm relationship with the president, never disclosed on air that he received legal services from Cohen.

Samuel Freedman, a professor at Columbia University's Graduate School of Journalism specializing in media ethics, said Hannity's omission was "clearly an ethical violation."

"It's so blatant, it's not even a hard call," Freedman said, adding that he thinks Fox should cut ties with Hannity over the potential conflict of interest.

"I don't think they'll do it, but I think they should fire him," Freedman said. "This is a major breach."

It appeared to be a moot point Tuesday, however. Fox News said it still backed Hannity despite learning about his dealings with Cohen on Monday.

"While Fox News was unaware of Sean Hannity's informal relationship with Michael Cohen and was surprised by the announcement in court yesterday, we have reviewed the matter and spoken to Sean and he continues to have our full support," the cable channel said in a statement.

When CNBC told Freedman that Fox News said it would continue supporting Hannity, he said it was "totally unsurprising."