14 of the 16 synonyms for unexpected begin with U, among them unannounced, unanticipated, unforeseen.
unannouncedunanticipatedunforeseenunheraldedunhopedunhoped-forunlooked for. See Thesaurus:surprisingunlooked-forunpredictedunprovided forunseenunthoughtunthought-ofupset