Treasury Secretary Steven Mnuchin sent a note to staff Friday informing them that his chief of staff, Eli Miller, will be leaving the Trump administration.

"For more than three years Eli Miller has been my closest advisor, both as the first finance hire on the campaign and subsequently at the Treasury Department. I write this note to inform our team of his planned upcoming departure from Treasury."

— Mnuchin's note, per two sources with direct knowledge.

Mnuchin told staff he was announcing the departure with "conflicting emotions."

Miller, 36, got his start in D.C. with former Speaker John Boehner's office before working for the Romney campaign in 2012, per Bloomberg News.