Wiktionary
bolt from the blue
n. A complete surprise; something totally unexpected.
Usage examples of "bolt from the blue".
Omally had penned Marchant up in his allotment shed, having read of a cyclist struck down one night by the proverbial bolt from the blue.
Druhallen calls it a 'bolt from the blue'a one-ended bolt of lightning.
The hint of smugness enraged Pappas and a suddenly realized solution came as a bolt from the blue.
In an instant like a bolt from the blue, like a thunderbolt from nowhere, that beautiful and defiant body had been dashed down the open well of the lift to death at the bottom.