Common Picture Book Opening Line: Once __

This page is the CodyCross answer for the clue below from Tundra and Taiga, Group 1683, Puzzle 2 (Short Summers).

Question is: Common Picture Book Opening Line: Once __

and the answer is: UPONATIME

Word Meaning:

UPON A TIME — (dated) At a certain time; at a particular time.

Definitions from Wiktionary.