CNN president Jeff Zucker announced his resignation on Wednesday for failing to disclose a romantic relationship with a colleague at the US cable television network.

"I certainly wish my tenure here had ended differently," Zucker said in a message to the network's employees. "But it was an amazing run. And I loved every minute."

Zucker, 56, said his resignation was effective immediately.

As head of the cable network since 2013, Zucker was one of the most powerful media executives in the United States.

In his message, Zucker said that as part of an investigation into a CNN anchor, he 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," he said. "I was required to disclose it when it began but I didn't. I was wrong."