Dr. Seuss. Theodor Seuss Geisel passed away in 1991. The last original book he released was in 1990 titled "Oh, the Places You'll Go!." Everyone including his wife and publisher assumed it was his last book. But it wasn't. They found this one in a box.

According to Wikipedia  the new book is based on manuscripts that his widow discovered while cleaning up his office shortly after his death in 1991 and then rediscovered it in 2013.

Random House associate publishing director Cathy Goldsmith says What Pet Should I Get? was likely written between 1958 and 1962. The book features the same brother and sister seen in Dr. Seuss’s 1960 classic One Fish Two Fish Red Fish Blue Fish. The publisher plans at least two more books, based on materials found in 2013 in the author’s home in La Jolla, California, by his widow and secretary.

All told, 45 Dr. Seuss books were published during Geisel’s lifetime, with another 16 released posthumously. Cumulative sales exceed 650 million copies, with the five bestsellers being Green Eggs and Ham (1960), The Cat in the Hat (1957), Dr. Seuss’s ABC (1963), One Fish, Two Fish, Red Fish, Blue Fish (1960), and Oh, the Places You’ll Go! (1990). Those five collectively have sold more than 73 million copies.

It's being reported that the first order for 'What Pet Should I Get?' has already gone from 500,000 printed copies to 1 million printed copies before it's even released.