A close advisor to Hillary Clinton is interviewed by the FBI regarding Clinton's private email system.

FOX's Jon Decker has more from the White House:

Cheryl Mills, a long-time senior aide to Hillary Clinton, and her lawyer both reportedly walked out of a recent interview with the FBI about Clinton's private email server.

The Washington Post said that Mills and her lawyer returned to the interview room after a brief absence.

The paper said that the FBI investigator's questions that caused Mills and her lawyer to walk out were related to the procedure used to produce emails for possible public release by the State Department.

Both Mills and her lawyer viewed these questions as off limits and covered under attorney-client privilege.

At the White House, Jon Decker, FOX News.