Englishundreamed of (also (British )undreamt of)
adjective
he raised the party's profile to undreamed-of heights:
unexpected, unforeseen, unanticipated, not bargained for, unhoped-for, unsought, unlooked-for, unpredicted;
unintentional, unintended, inadvertent, unplanned, unpremeditated, unwitting, fortuitous, chance, coincidental, serendipitous, random, fluky;
sudden, abrupt, surprise, surprising, without warning, without notice, startling, astonishing, out of the blue.
▷antonyms deliberate, planned.