Lockheed Martin CEO Robert Stevens said Friday that his named successor has been fired for allegedly engaging in an affair with a subordinate, and announced a new replacement to run the world’s largest defense firm once he steps down at the end of the year.

Chris Kubasik, the vice chairman, president and chief operating officer, complied with a request from Lockheed Martin’s Board of Directors to resign effective immediately for violating the company’s code of conduct, Stevens said. Lockheed Martin launched an outside investigation into Kubasik’s actions after an employee came forward and divulged the alleged relationship in late October, he said.

“While I am deeply disappointed and saddened by Chris’ actions, which have been inconsistent with our values and standards, our swift response to his improper conduct demonstrates our unyielding commitment to holding every employee accountable for their actions,” Stevens told reporters on a conference call late Friday afternoon.

Kubasik, 51, had been slated to replace Stevens, who plans to retire, Jan.1. The company board’s elected Marillyn A. Hewson, currently the executive vice president for electronic systems, to replace Kubasik, who is married, as COO and succeed Stevens at the beginning of the year, the CEO said.

The employee who revealed the alleged indiscretion was not the subordinate involved with Kubasik, Stevens said. The subordinate is also no longer employed by Lockheed Martin, he added.

Citing privacy considerations, Stevens would not say when the alleged relationship began, how long it lasted, or whether Kubasik admitted to it.

Stevens said he will proceed with the leadership transition already underway by working closely with Hewson, 58, characterizing the Kubasik situation as a “temporary distraction.”

“I don’t believe the company’s in a crisis,” he told reporters. “I believe we are changing course.”

Lockheed Martin’s strong leadership team and “robust” succession plan allowed the board to react quickly to the situation and choose a new successor, Stevens said.

“Marillyn is an exceptional leader with impeccable credentials and deep knowledge of our business, customers, shareholders and employees,” he said.