"The Return of the Clockwork Smurf" is not based on any "Johan et Pirlouit" ("Johan and Peewit" in English) comic story. It is an original story due in part that King Gerald, Clockwork Smurf, and Gerald's evil uncle Leopold are creations of Studio Peyo for the cartoon series.
One of the few episodes to be animated at Hanna-Barbera Australia, albeit uncredited.
This episode reveals that King Gerard and Princess Sabina are cousins/relatives.
This was King Gerard's only appearance in the Johan and Peewit episodes along with being the only episode where they interact with each other.