unannounced vs unforeseen

unannounced

adj

  • Not announced beforehand. 

unforeseen

adj

  • Not foreseen. 

  • Not expected. 

noun

  • An event, incident, cost, etc. that was not foreseen. 

How often have the words unannounced and unforeseen occurred in a corpus of books? (source: Google Ngram Viewer )