Horse & Pony Books:
(SCHOLASTIC PB [USA] 1976)
Reprinted a number of times in paperback by Scholastic.
SUMMARY: "Run, Star, run! Get out as fast as you can!" Panic stricken, the horse obeys, racing wildly, blindly through the flames. To Jago, a lonely gypsy boy, Flaming Star was a loving and trusting friend. To Flaming Star, Jago was the whole world. Then a tragic fire separated them..would the pair ever see each other again?
Fairly easy to find in the USA. However can be hard to find elsewhere.