Source : WordNet®

out of the blue
     adj : not anticipated; "unanticipated and disconcerting lines of
           development"- H.W.Glidden; "unforeseen circumstances";
           "a virtue unlooked-for in people so full of energy";
           "like a bolt out of the blue" [syn: {unanticipated}, {unforeseen},
            {unlooked-for}, {out of the blue(p)}]
     adv : in a way that was not expected; "her brother showed up at
           the wedding out of the blue" [syn: {unexpectedly}]