CNN President Jeff Zucker Protected Chris Cuomo. Then Came a U-Turn.

Everything changed this past week. New information surfaced—including detailed records from the New York attorney general’s office, a report from the law firm Cravath Swaine & Moore and an unrelated allegation of sexual misconduct—that sealed Chris Cuomo’s fate.

Mr. Zucker was taken by surprise by the attorney general’s report, and felt Mr. Cuomo misled him, according to people familiar with the situation. On Saturday he completed a U-turn, firing Mr. Cuomo on a call, one of the people said.

Mr. Cuomo has apologized for advising his brother, who was embroiled in a significant story CNN was covering. A spokesman for Mr. Cuomo said in a text message on Sunday: “Mr. Cuomo has the highest level of admiration and respect for Mr. Zucker. They were widely known to be extremely close and in regular contact, including about the details of Mr. Cuomo’s support for his brother. There were no secrets about this, as other individuals besides Mr. Cuomo can attest.”

CNN said in a written statement it is disappointed with Mr. Cuomo’s characterization of events. “He has made a number of accusations that are patently false,” the network said. “This reinforces why he was terminated for violating our standards and practices, as well as his lack of candor.”

Staffers at CNN have been surprised by the network’s handling of the controversy from the beginning. When the revelations first surfaced, some employees were taken aback that there wasn’t disciplinary action, people inside the network said. After Mr. Zucker publicly defended Mr. Cuomo for months, some staffers figured the anchor would survive any fallout, and were equally surprised that Mr. Zucker reversed his position, the people said. Some on-air and behind-the-scenes staffers had said Mr. Cuomo could be back on air in January.

Mr. Zucker’s decision to fire one of CNN’s most-watched anchors creates a hole in the network’s prime-time lineup. Like every cable news channel, CNN is grappling with a viewership slump compared with last year, when the fractious 2020 presidential election and its aftermath drove ratings to new heights. The network is also in the midst of launching a streaming service, CNN+.

Mr. Zucker has been one of Chris Cuomo’s biggest champions at CNN. One of Mr. Zucker’s first moves when he arrived at CNN in 2013 was to recruit Mr. Cuomo from ABC News to co-anchor a morning news show. Mr. Zucker promoted Mr. Cuomo to prime time in 2018, giving him the coveted 9 p.m. hour and putting him against two cable-news heavyweights, Rachel Maddow at MSNBC and

Sean Hannity

at Fox News. A year later, Mr. Zucker praised Mr. Cuomo’s pugilistic instincts to the Hollywood Reporter, calling him “the perfect cable news anchor.”

That professional relationship eventually came under strain. Allegations that Mr. Cuomo aided his brother’s advisers came to light in May in a Washington Post article. It was a sensitive moment for CNN, whose parent company,

AT&T Inc.,

T 1.78%

had just reached a deal to merge its media assets with rival

Discovery Inc.

DISCB -11.57%

Mr. Zucker hadn’t yet announced his eventual decision to stay on to steer the network through the merger.

As months went by, Mr. Cuomo remained on air, even after he continued to make headlines and create headaches for Mr. Zucker. In August, New York Attorney General Letitia James released a report that confirmed Mr. Cuomo had aided then-Gov. Cuomo’s response to his scandal.

The following month, Shelley Ross, a former producer at ABC News, accused Mr. Cuomo of touching her inappropriately in 2005 at a party for staffers at that network. Mr. Cuomo, who worked at ABC at the time, said in a written statement that the incident wasn’t sexual in nature and that he had apologized to Ms. Ross.

Mr. Zucker’s public support of Mr. Cuomo began to show cracks on Nov. 29, when Ms. James’s office released records that provided greater detail about Mr. Cuomo’s efforts to aid his brother. The records showed Chris Cuomo texted one of his brother’s former advisers,

Melissa DeRosa,

telling her he had “a lead on the wedding girl” shortly after the New York Times published a report that quoted a woman who said Andrew Cuomo touched her inappropriately at a wedding.

The records also include an interview of Chris Cuomo by investigators in which the anchor said he contacted other journalists to figure out whether stories about Andrew Cuomo’s conduct were in the works. “When asked, I would reach out to sources, other journalists, to see if they had heard of anybody else coming out,” Chris Cuomo told investigators, according to a transcript of the interview released by Ms. James’s office.

Dennis Vacco,

who served as New York attorney general from 1995 to 1999, said in an interview that it was unusual for Ms. James’s office to release the records from the investigation, but not improper. “It’s certainly unique,” Mr. Vacco said.

The revelations in the documents wounded Mr. Zucker, an executive who prides himself on developing employee relationships based on trust, people close to the network boss said.

CNN suspended Mr. Cuomo on Tuesday, the day after the documents became public, and hired law firm Cravath Swaine & Moore to investigate the matter. On Friday, Cravath informed CNN that the network had cause to fire Chris Cuomo after finding that he had violated the network’s standards and practices.

Meanwhile, Mr. Zucker had become aware of another allegation of sexual misconduct against Mr. Cuomo from one of his former colleagues at ABC News. Debra Katz, a lawyer for the former staffer, said her client—who wants to remain anonymous—was motivated to come forward by Chris Cuomo’s on-air statements in support of victims of sexual harassment.

“Hearing the hypocrisy of Chris Cuomo’s on-air words and disgusted by his efforts to try to discredit these women, my client retained counsel to report his serious sexual misconduct against her to CNN,” Ms. Katz said in a written statement.

Through a spokesman, Chris Cuomo denied allegations of sexual misconduct. When it announced Chris Cuomo’s firing on Saturday, CNN said it would investigate the allegation of misconduct “as appropriate.”

—Jimmy Vielkind contributed to this article.

Write to Benjamin Mullin at Benjamin.Mullin@wsj.com and Joe Flint at joe.flint@wsj.com