Bob Woodward’s 18th book, “The Last of the President’s Men,” will be out Oct. 13 — spilling the secrets of Alexander Butterfield, a West Wing aide who oversaw the installation of President Richard Nixon’s fateful taping system, Simon & Schuster announced Thursday.

Woodward interviewed Butterfield, now 89, for 46 hours over the course of the year. Butterfield spent four years in the Nixon West Wing as deputy to White House Chief of Staff H.R. Haldeman, three of them in an office adjoining the Oval Office.

“Butterfield was regularly the first to see Nixon in the morning and the last at night, the constant insider and ultimately the most dangerous witness,” the announcement says.