Upvote:1
As stated in Timatic, the database used by airlines:
Visa required [for Bulgaria], except for passengers with a C visa issued by Croatia, Cyprus, Romania or a Schengen Member State valid for the period of intended stay. They are visa exempt for a maximum stay of 90 days
So your Schengen visa only needs to be valid. It doesn't matter if you used it to enter the Schengen Area before Bulgaria or not.
So: