CNN President Jeff Zucker resigned from the TV news organization, citing his failure to disclose a consensual relationship with a close colleague, and cutting short a nine-year tenure during which he helped transform the network’s role in the cable-news landscape.

Mr. Zucker’s abrupt departure comes as CNN is grappling with declining ratings as it also prepares to jump into the streaming wars with a new subscription service, CNN+, under future owner Warner Bros. Discovery.

“As...

CNN President Jeff Zucker resigned from the TV news organization, citing his failure to disclose a consensual relationship with a close colleague, and cutting short a nine-year tenure during which he helped transform the network’s role in the cable-news landscape.

Mr. Zucker’s abrupt departure comes as CNN is grappling with declining ratings as it also prepares to jump into the streaming wars with a new subscription service, CNN+, under future owner Warner Bros. Discovery.

“As part of the investigation into Chris Cuomo’s tenure at CNN, I was asked about a consensual relationship with my closest colleague, someone I have worked with for more than 20 years,” Mr. Zucker wrote in an email he sent to staff on Wednesday. “I acknowledged the relationship evolved in recent years. I was required to disclose it when it began but I didn’t. I was wrong.”

During a web call on Wednesday afternoon, Jason Kilar, chief executive of CNN parent WarnerMedia, told a group of CNN brass still reeling from news of Mr. Zucker’s departure that a trio of CNN executives would lead the network on an interim basis, according to people familiar with the situation. Michael Bass, executive vice president of programming, Amy Entelis, executive vice president for talent, and executive vice president Ken Jautz will be in charge of CNN until a new executive is named, the people said.

The colleague Mr. Zucker referred to in his email is Allison Gollust, an executive vice president and chief marketing officer at CNN. In a statement, Ms. Gollust, who will continue in her job, said that she and Mr. Zucker have been friends for over 20 years and said that the relationship changed during the Covid-19 pandemic.

“I regret that we didn’t disclose it at the right time,” Ms. Gollust said. “I’m incredibly proud of my time at CNN and look forward to continuing the great work we do everyday.”

Both Ms. Gollust and Mr. Zucker are divorced.

‘I certainly wish my tenure here had ended differently,’ Jeff Zucker said in an email to staff.

Photo: Mike Coppola/Getty Images

WarnerMedia, which is a unit of AT&T Inc., says it has a policy that prevents employees from supervising co-workers with whom they have a personal relationship. The policy states that employees must inform the company if they are in a position to influence the advancement of an employee they have a relationship with before taking any action.

Mr. Zucker, who is 56 years old, disclosed the relationship with Ms. Gollust to WarnerMedia in recent days during an investigation into former CNN host Chris Cuomo, people familiar with the matter said. Mr. Cuomo was fired by CNN in December after the investigation found he improperly helped his brother, former New York Gov. Andrew Cuomo, respond to accusations of sexual misconduct.

New York Gov. Andrew Cuomo resigned Tuesday, one week after a state report found he had sexually harassed multiple women. His resignation cuts short a third term as governor that was marred by controversy. Cuomo has denied all allegations of sexual harassment. Photo: Office of the Governor of New York The Wall Street Journal Interactive Edition

In the past week, Mr. Kilar learned that Mr. Zucker disclosed the relationship as part of the investigation and quickly decided Mr. Zucker should step down, some of the people said. Mr. Zucker then submitted his resignation, they said.

Mr. Kilar, who traveled to Washington, D.C., on Wednesday to address CNN staff, faced many questions from employees who felt Mr. Zucker didn’t get a second chance after disclosing his relationship with Ms. Gollust. Mr. Kilar declined to answer questions about the timeline of Mr. Zucker’s departure, though he said that he followed a process “with an appropriate sense of urgency.”

“I wasn’t focused on the business of it all,” Mr. Kilar said. “My focus, first and foremost, are on the values that we stand for as a company.”

Mr. Kilar said there are no plans to issue additional information about the investigation, which he said is complete.

During the question-and-answer session, anchor Jake Tapper said that Mr. Cuomo hired a lawyer who seemed eager to leak damaging information about Mr. Zucker unless they gave Mr. Cuomo severance.

“An outside observer might say, ‘Well, it looks like Chris Cuomo succeeded,’” Mr. Tapper said. “He threatened Jeff. Jeff said we don’t negotiate with terrorists. And Chris blew the place up. How do we get past that perception that this is the bad guy winning?”

A spokesman for Mr. Cuomo declined to comment. A spokeswoman for WarnerMedia said that the company doesn’t comment on investigations.

AT&T is preparing to spin off CNN parent WarnerMedia and merge it with Discovery Inc. to form a new company, Warner Bros. Discovery. Mr. Zucker had indicated he planned to stay at CNN at least through the closing of the deal.

A former wunderkind producer of NBC’s “Today” show, Mr. Zucker rose through the media industry’s ranks over a three-decade-plus career. He became chief executive of NBCUniversal, leaving after Comcast Corp. took control in 2011.

Mr. Zucker and Ms. Gollust have worked closely together at different companies for years. Ms. Gollust was a communications executive at NBC News when Mr. Zucker was NBCUniversal’s CEO, and she joined CNN after Mr. Zucker was named president of that network in 2013.

Ms. Gollust has also worked for former Gov. Andrew Cuomo.

After joining CNN, Mr. Zucker quickly put his stamp on the network, reshuffling the anchor lineup and hiring journalists such as Mr. Tapper, Alisyn Camerota, Chris Cuomo and Brian Stelter.

During the run-up to the 2016 election, Mr. Zucker was criticized for giving then-candidate Donald Trump too much airtime. The network enjoyed a ratings surge during the Trump years, as Mr. Zucker steered coverage that was critical of the former president.

In 2019, Mr. Zucker was promoted to take on oversight of WarnerMedia’s sports properties, in addition to his role at CNN. More recently, CNN’s viewership has fallen off amid a wider decline in cable ratings.

As CNN’s business head and de facto programmer-in-chief, Mr. Zucker has been a hands-on leader, running daily news calls and spearheading contract negotiations with anchors. His departure leaves a hole at the network, which is preparing to launch CNN+, an ambitious direct-to-consumer streaming service that Mr. Zucker championed.

Don Lemon, the host of “Don Lemon Tonight,” said in an interview that anchors would miss encouraging texts from Mr. Zucker during commercial breaks.

“Jeff has been one of the most important people for me, personally and professionally, for the last decade,” Mr. Lemon said. “He’s important to me. Not only that, he’s important to just about everyone at the network, especially the on-air talent.”

Write to Benjamin Mullin at Benjamin.Mullin@wsj.com