coincidence · noun C or U /koʊˈɪn.səd.əns/
coincidence
B2 when two very similar things happen at the same time but there is no reason for it
Dictionary examples:
You chose exactly the same wallpaper as us - what a coincidence!
Just by coincidence I met my old friend and classmate again fifty years later.
It was pure coincidence that we met.
Learner example:
What a coincidence, don't you think so? (First Certificate in English; B2; Portuguese)