once upon a time vs subsequently

once upon a time

adv
  • A long time ago; at some time in the past (a traditional beginning of children's stories, especially fairy tales). 

subsequently

adv
  • Following, afterwards in either time or place. 

  • Accordingly, therefore (implying a logical connection or deduction), consequently. 

How often have the words once upon a time and subsequently occurred in a corpus of books? (source: Google Ngram Viewer )