Based on the Brothers Grimm fairy tale "The Donkey", per Wikipedia.
Carter's "rendering of the frog-prince motif" per Kirkus Reviews, which covers the Keith illustrations too.
Not based closely on Grimm. Carter's donkey prince must eat a magic apple, rather than win the love of a human princess.
Publication date from contemporary review by Kirkus (see Title Reference)
Stated "First U.S. Printing"
Price from front DJ flap.
Lists SBNs for both trade edition (shown here) and Library edition (671-65148-X).