un ‧ fore ‧ seen /ˌʌnfɔːˈsiːn◂ $ -fɔːr-/ BrE AmE adjective
an unforeseen situation is one that you did not expect to happen
unforeseen circumstances/events/changes etc
Due to unforeseen circumstances, the play has been cancelled.
unforeseen problems/difficulties/delays
unforeseen delays in supplying the equipment