ex improviso
/ˌɛks ɪmprəˈvʌɪzəʊ/adverb
Unexpectedly, suddenly, without warning. In later use chiefly in legal contexts.
Origin
Early 16th century. From classical Latin ex imprōvīsō suddenly, unexpectedly from ex + imprōvīsō, ablative of imprōvīsum, use as noun of neuter of imprōvīsus.