CNN Worldwide President Jeff Zucker said Wednesday that he is resigning, effective immediately.

Zucker said in a memo, "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. I acknowledged the relationship evolved in recent years. I was required to disclose it when it began but I didn't. I was wrong. As a result, I am resigning today."

Zucker did not name his colleague in the memo, but the relationship is with Allison Gollust, the Chief Marketing Officer for CNN. Gollust is remaining at CNN.

In a memo of her own, Gollust said, "Jeff and I have been close friends and professional partners for over 20 years. Recently, our relationship changed during COVID. I regret that we didn't disclose it at the right time. I'm incredibly proud of my time at CNN and look forward to continuing the great work we do everyday."

Zucker took over CNN in 2013, at a time when industry observers said the network was facing an identity crisis.

Zucker revamped the network's programming. A veteran of NBC, where he climbed from a producer on the "Today" show to President of the entire network. Zucker brought an eye for news and talent. He also brought a hands-on management style and gained the trust and respect of talent and staffers throughout the network.

In recent years, Zucker led the network as it faced sustained attacks from former President Trump and his supporters. Under Zucker, CNN adopted a "Facts First" slogan and approach to the news and was unrelenting in calling out Trump for his lies.

The approach turned Zucker into a villain for Trump, with the then-President lashing out at him during his years in office. Zucker also became a regular boogeyman in right-wing media, with Fox hosts viciously attacking him in prime time. It was all evidence of Zucker's larger-than-life status in the news business and influence over the broader discourse in American politics.

News of Zucker's resignation left staffers inside the network in shock. Employees at the company learned of his sudden departure in the memo Zucker sent to staff shortly after 11 a.m. ET.

In an email to staffers sent shortly after Zucker's, Jason Kilar, the CEO of CNN parent WarnerMedia, said, "I have accepted Jeff Zucker's resignation as Chairman of WarnerMedia News and Sports, and President of CNN Worldwide. We thank Jeff for his contributions over the past 9 years."

Kilar added, "We will be announcing an interim leadership plan shortly. Both of these organisations are at the top of their respective games and are well prepared for their next chapters."

Zucker is one of the most powerful and influential executives in the media industry. His abrupt resignation comes as WarnerMedia is in the process of merging with Discovery. It also comes as CNN plans to launch a streaming service, CNN+, in the Spring.

This is a developing story. Check back for more.