[out of the blue] or [out of a clear sky] or [out of a clear blue sky] {adv. phr.}, {informal} Without any warning; by surprise; unexpectedly.
* /At the last minute Johnny came out of the blue to catch the pass and score a touchdown./* /The cowboy thought he was alone but suddenly out of a clear sky there were bandits all around him./
Syn.: OUT OF NOWHERE. Compare: BOLT FROM THE BLUE.