Formerly a fairy-tale start (4)
I believe the answer is:
once
This clue is a double definition.
'formerly' is the first definition.
(I know that formerly can be written as once)
'a fairy-tale start' is the second definition.
(I've seen this in another clue)
(Other definitions for once that I've seen before include "... upon a time for the storyteller" , "In days gone by" , "At some time past" , "One-time musical film and song" , "Sometime" .)