How Long-Lost Dr. Seuss Book Released Today Was Discovered A manuscript by Dr. Seuss was discovered in a box years after his death.

 -- Among Theodor Seuss Geisel's things set aside by his widow after his death was an unknown manuscript that would become a book being published posthumously under his pen name, Dr. Seuss.

The classic children's author died on Sept. 24, 1991 at the age of 87. At the time, his widow, Audrey Geisel, was renovating their home in La Jolla, California, outside San Diego, and placed some of his work in a box. Years later, in 2013, she and his long-time assistant, Claudia Prescott, decided to have his drafts and sketches in the box appraised and discovered a project that would become his 46th book.

Released today, "What Pet Should I Get?" follows Dr. Seuss best-sellers such as "Green Eggs and Ham" and "The Lorax." His first major success was "The Cat in the Hat," published in 1957. His final book before his death, “Oh, the Places You’ll Go!” was published in 1990.

Geisel’s widow, 93, called the discovery of what would become the new book “undeniably special” but not surprising. Audrey Geisel is helped by Prescott, who began assisting the author in 1972, in running Dr. Seuss Enterprises.

“Ted always worked on multiple projects and started new things all the time -- he was constantly drawing and coming up with ideas for new stories,” she said, according to a statement by Random House in February.

The original manuscript was a series of black-and-white illustrations with separate pieces of text taped by the drawings, photos show. The book's main characters are the brother and sister in "One Fish Two Fish Red Fish Blue Fish." In February, Random House announced plans to publish "What Pet Should I Get?" and two other upcoming titles by Seuss.

Susan Brandt, president of licensing and marketing for Dr. Seuss Enterprises, L.P., described her reaction to the discovery.

“We had no idea what we were in store for when Claudia notified us of the materials discovered in Ted’s home,” she said in the statement. “Pages and pages of manuscripts and sketches were laid out on the big glass dining room table. It was truly a magical moment, and we immediately knew this was more than just a box of sketches.”

The first printing of "What Pet Should I Get" is expected to be a major publishing event today with one million copies.

Calls to Dr. Seuss Enterprises for additional information were not immediately returned.