Jeff Zucker Resigns from CNN Over Undisclosed Relationship with Colleague

Jeff Zucker just dropped a bombshell at CNN -- he's resigning as network president, because of a romantic relationship he kept hidden ... one that only came to light during the Chris Cuomo investigation.

Jeff, who is also stepping down from his post as chairman of WarnerMedia's news and sports division, blasted out a memo to co-workers Wednesday ... saying that during the Cuomo probe he was asked "about a consensual relationship with my closest colleague, someone I have worked with for more than 20 years."

He doesn't say the relationship itself is the problem, he says it's because he lied. Jeff wrote, "I acknowledged the relationship evolved in recent years. I was required to disclose it when it began but I didn't. I was wrong."

Jeff did not name the colleague who he had a relationship with in his memo ... but CNN says the person is Allison Gollust, the network's chief marketing officer.

CNN says Allison is keeping her job.

It's interesting the Cuomo investigation also took down Zucker ... remember, Jeff initially stood by Chris when the anchor came under fire for advising aides to his brother, former New York Gov. Andrew Cuomo, on how to fend off a sexual harassment scandal.

But, as the investigation dragged on, Jeff eventually distanced himself from Chris and dropped his support.