NEW YORK — The author of the million-selling business book "Who Moved My Cheese?" was writing a sequel at the time of his death last year.

Spencer Johnson's "Out of the Maze: A Story About the Power of Belief" is coming out Sept. 4, Portfolio told The Associated Press on Tuesday. Portfolio is an imprint of the Penguin Publishing Group.

The release of "Out of the Maze" coincides with the 20th anniversary of "Who Moved My Cheese?" — Johnson's brief fable about the need for flexibility that featured two mice, Sniff and Scurry, and two people, Hem and Haw. Johnson, who died of cancer in July 2017 at age 78, had been working on a story with some of the same characters. He had nearly finished the book and was discussing it with his literary representative, Robert Barnett, and with Portfolio President Adrian Zackheim.

"I knew that Spencer was not well when we had our last editorial conversation about the book, but I wasn't aware of the gravity of his illness," Zackheim said in a statement. "I was shocked when I learned that he had died just a few days after we talked about revisions to the manuscript. Fortunately, Spencer bequeathed a wonderful book to us."

Johnson's other books included "The One Minute Manager" and "The Precious Present."