The United States Air Force chief of staff announced on Monday that he planned to retire in the coming months, but did not provide a reason.

The announcement by General David Allvin was a surprise, as he will have served just two years out of the typical four-year assignment by the time he retires.

“I’m grateful for the opportunity to serve as the 23rd Air Force Chief of Staff, and I’m thankful for (Air Force) Secretary Meink, Secretary Hegseth and President Trump’s faith in me to lead our service,” Allvin said in a statement.

Allvin said he will retire on or about November 1.

It was unclear whether Allvin chose to retire or was asked to by Pentagon leaders such as Defence Secretary Pete Hegseth. The Office of the Secretary of Defence did not immediately respond to a request for comment.

Hegseth has fired a number of senior military officials since taking office in January, including the chairman of the Joint Chiefs of Staff, the head of the U.S. Navy and the Judge Advocates General for the Army, Navy and Air Force.