'unannounced' definitions:

Definition of 'unannounced'

From: WordNet
adjective
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]

Synonyms of 'unannounced'

From: Moby Thesaurus