bolt from (out of) the blue
An unexpected event that strikes like lightning from the sky: “He had been with the company for eighteen years; when he was fired, it must have felt like a bolt from the blue.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.