The chief of staff for Secretary of Defense Mark Esper has resigned. The resignation follows a controversial attack that killed Iranian General Qassem Soleimani. It remains unclear if the resignation was related to the attack.

According to Fox News:

Eric Chewning, the chief of staff to Defense Secretary Mark Esper, is resigning and will be leaving his post at the end of January, the Defense Department announced Monday.

Chewning has been in his role since January 2019, after starting with the Department in October 2017 as the deputy assistant secretary of defense for industrial policy. He now plans on returning to the private sector, according to Pentagon press secretary Alyssa Farah.

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“I’m grateful for Eric’s professionalism, judgment, and leadership over the last seven months as I moved into the secretary of defense role,” Esper said in a statement. “In an incredibly demanding job, Eric has been a source of calm and tireless work. He will be missed by all. We wish him all the best upon his return to the private sector.”

The move comes as the department is in the midst of dealing with increased hostilities with Iran. A U.S. airstrike killed Gen. Qassem Soleimani, leading the Islamic nation to vow revenge. President Trump has threatened further action if Iran indeed retaliates.

Jen Stewart, who has been serving as the minority staff director for the House Armed Services Committee will take over for Chewning and Esper has touted her qualifications.