Unforeseen
Part of speech: adjective
Definition: not foreseen. not expected.
Example sentence: I want diversity to be at the very heart of the BBC and not delivered by some other party with increased government interference, bureaucracy and unforeseen consequences.
Sudden
Part of speech: adjective
Definition: Happening quickly and with little or no warning.
Part of speech: adverb
Definition: Suddenly.
Example sentence: I was born fat and have always been, which was just fine and even healthy and cute until I turned ten or so. Puberty hit like a hurricane and brought a new set of rules. All of a sudden it was my fault I was chubby.