WordNet (r) 3.0 (2006):

unheralded
    adj 1: without warning or announcement; "they arrived
           unannounced"; "a totally unheralded telegram that his
           daughter...died last night"- M.A.D.Howe [syn:
           unannounced, unheralded, unpredicted]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "unheralded":
   extraordinary, improbable, more than expected, out-of-the-way,
   past expectation, sudden, surprise, unannounced, unanticipated,
   undivined, unexpected, unforeseeable, unforeseen, unguessed,
   unhoped for, unpredictable, unpredicted, unprepared for,
   without warning