by an accidental and strange similarity; by an unplanned pairing of events or occurrences. We just happened to be in the same place at the same time by coincidence.By coincidence, the circus was in town when I was there. I'm glad because I love circuses.
by coincidence
Through an accidental simultaneous occurrence, as in By coincidence both researchers discovered the same solution. [Mid-1600s] Also see by chance.