CNN President Jeff Zucker “stunned” colleagues on Wednesday by announcing his sudden resignation, writing in a memo that he had failed to disclose a romantic relationship with another senior executive at CNN.

Zucker ends a nine-year tenure as the network’s president and chairman of WarnerMedia’s news and sports division.

In the memo, Zucker said that his relationship came up during the investigation into disgraced ex-CNN anchor Chris Cuomo’s actions to squash the sexual harassment allegations leveled at his brother, former New York Gov. Andrew Cuomo.