(WASHINGTON) — James Anderson, the acting under secretary for policy, who is considered to be among the Pentagon’s most important officials, has left the Department of Defense.

A defense official confirmed that Anderson resigned Tuesday and confirmed the contents of his resignation letter which was published by Politico.

A former defense official told ABC News that Anderson was asked to submit a resignation letter, which essentially means he was being fired. The Pentagon is not releasing the letter.

Anderson had been filling in as the acting policy chief since February when John Rood was fired by the Trump administration over policy disagreements.

The Pentagon is not confirming who Anderson’s successor will be.

Anderson’s departure follows President Donald Trump’s decision to fire Defense Secretary Mark Esper on Monday.

This is a developing news story. Please check back for updates.

Copyright © 2020, ABC Audio. All rights reserved.