... upon a time, fairytale opening (4)
I believe the answer is:
once
(Other definitions for once that I've seen before include "In times past" , "Cone (anag.)" , "Just as a single occurrence" , "in bygone era" , "Formerly - not repeated" .)
I believe the answer is:
once
(Other definitions for once that I've seen before include "In times past" , "Cone (anag.)" , "Just as a single occurrence" , "in bygone era" , "Formerly - not repeated" .)