Auzou Book for azuro has disappeared

While Azuro receives an unexpected visit from his best friend Morgane, she brings him a letter she found on the doorstep of the blue dragon. Intrigued, Azuro opens the letter and WHOOSH, shrinks... He ends up smaller than the blades of grass in the garden... Then, as the spell's effect wears off and Azuro returns to his normal size, he suddenly multiplies, and soon five Azuros are playing in the garden... But who could have cast a spell on Azuro?