Department of Defense chief of staff Rear Adm. Kevin Sweeney announced Saturday that he is resigning from his post at the Pentagon.

"After two years in the Pentagon, I've decided the time is right to return to the private sector,” Sweeney said in a statement. “It has been an honor to serve again alongside the men and women of the Department of Defense.”

Just last month, former Secretary of Defense Jim Mattis resigned on principle after President Trump announced his intent to withdraw troops from Syria. Since then, other administration officials including Brett McGurk, the special presidential envoy for the global coalition to counter ISIS, and Pentagon spokeswoman Dana White have also departed their posts within the administration.

Mattis, who worked with Sweeney when he led the U.S. Central Command, tapped Sweeney to be his chief of staff in Jan. 2017. In his role at the Pentagon, Sweeney advised and counseled Mattis.

During his time as an active-duty service member, Sweeney was the commanding officer of the USS Cole and was in charge of overseeing restoration of the destroyer after the October 2000 terrorist attack, among other notable tours of duty.

Sweeney, who attended the U.S. Naval Academy and graduated in 1982, retired from the military in 2014 and then served as vice president of Track Patch 1 Corporation, a company that builds technology to monitor those suffering from Alzheimer’s dementia. He also was interim president and CEO of Hampton Roads Economic Development Alliance, a joint public-private corporation designed to promote the Virginia region globally as an area for business investment.

Deputy Defense Secretary Patrick Shanahan is now serving as acting secretary of defense. Trump said late last month that Shanahan may remain in the position for the “for a long time.”