Beloved children’s author and avid hat collector Theodore Geisel published his first book, And to Think That I Saw It on Mulberry Street, in 1937. Though Geisel was his real name, you probably know him better as Dr. Seuss: the late, great creative force behind Cat in the Hat and Green Eggs and Ham.

Just when fans thought they had read everything he had ever written, a piece of good news arrived just ahead of Dr. Seuss Day, which will mark the 115th anniversary of the writer’s birth on March 2. A brand new Seuss book, titled Dr. Seuss’s Horse Museum, will be posthumously published by Random House this September.

The never-before-seen text, with pictures by Andrew Joyner, is based on an original Seuss manuscript and sketches that were found in the author’s former home in La Jolla, California, in 2013. (The manuscript for what would become the 2015 bestseller What Pet Should I Get? was also unearthed at the same time.)

At its core, Horse Museum is about “creating and experiencing art,” according to the publisher. In the story, an “affable horse” character takes students on a tour of a museum that showcases the ways in which horses were depicted by famous artists—from Pablo Picasso to Jackson Pollock—throughout history. Joyner’s drawings are reminiscent of Seuss’s signature style, and full-color photographs of the “real-life” artworks are also shown alongside the illustrations, making it a great children’s introduction to art history.

“I remember fondly the days when Ted would come to Random House to hand-deliver his latest work, which included reading aloud to staff gathered in a conference room,” Dr. Seuss’s former art director, Cathy Goldsmith, said in a statement. “Poring over the manuscript and Ted’s original sketches for Dr. Seuss’s Horse Museum brought me right back to those days, and I continue to be so honored to bring his brilliant work to today’s young readers.”

The book will be released September 3, but you can pre-order it now from Amazon for $19.