From Longman Dictionary of Contemporary Englisha bolt from/out of the bluea bolt from/out of the blueEXPECTnews that is sudden and unexpected Was this money a bolt from the blue or did you know you were going to get it? → bolt
Examples from the Corpus
a bolt from/out of the blue• Even so, dismissal should never come as a bolt from the blue, however exalted your place in the corporate hierarchy.• The Mishcon job came like a bolt from the blue.• Inspiration hit me like a bolt from the blue on the way home. 