Andrew Peek, a White House adviser on Russia and Europe, was escorted out of the White House Friday amid a security-related investigation.

According to Bloomberg, Peek was put on leave and has now left the National Security Council position vacated by both Fiona Hill and Tim Morrison, both of whom testified during the House impeachment inquiry. His departure marks the third time the position has been vacant in less than a year.

He formerly served as deputy assistant secretary of state for Iraq and Iran.

Per the Hill, he was supposed to accompany President Donald Trump to the World Economic Forum in Davos, Switzerland next week.

The reason for Peek’s departure and the related investigation is unclear, as the NSC has maintained that it “does not discuss personnel matters.”