What is the adjective formed from fable?

The adjective of the Word fable is fabled.

Fable means a mythical story that is ususally short and teaches a lesson (e.g. Aesop's Fables).

Fabled means something that is famous or well known usually for its storylike or usually unbelivable aspects; legendary; fictitious (e.g. The fabled lands of the Elysian Fields.)