out of the blue

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.