If you walk into somebody in a place where you didn’t expect him, you say:
Hé, dat is toevallig!
What a coincidence!It also can be used ironically, when it isn’t really a surprise or if there is something fishy about it ….
Dat is wel heel toevallig
Well, well, what a coincidence…
We also use this word for ‘incidentally’ :
Weet iemand toevallig waar Jan is gebleven?
Does anybody incidentally know where Jan has gone?