Robert Caro offered an update on the long-awaited final installment of his five-volume biography of President Lyndon B. Johnson.

The Years of Lyndon Johnson series began in 1982 with The Path to Power and continued with Means of Ascent (1990), Master of the Senate (2002), and The Passage of Power (2012). Among the most revered works of contemporary nonfiction, they’ve won a Pulitzer Prize, a National Book Award, and two National Book Critics Circle Awards between them.

The fifth volume, currently untitled, will cover Johnson’s life from 1964, the year of his election victory over Barry Goldwater, through his death in 1973. Caro is 90, and some readers have expressed concern that he might not complete the book in his lifetime.

Caro was interviewed on C-SPAN by Peter Slen, who asked Caro if he would walk him through notes on a corkboard in his office.

“Well, I don’t want to do that,” Caro replied. “What it is is my outline in great detail, the whole book.…I have written 983 pages. That is this, OK? This is the rest of the book. The way I am, I have to have it all outlined. I can’t just start writing. I have to know the beginning to the end.”

Caro said he has kept his work on the fifth book secret.

“Nobody sees anything until it is all done,” he said. “I do not show it early. Only one time in all these years, I ran out of money doing the Johnson books…so I had to ask for more money. And then he said, ‘I have to see something,’ so I gave him something written up to that point. That is the only time I ever showed anybody.”

Slen asked Caro when readers could expect the new book to be published.

“Fair question,” Caro said after a brief pause, but did not offer an answer.

Michael Schaub is a contributing writer.