短语 a bolt from the blue, 意思是发生了完全意想不到的事情，晴天霹雳。

例句

The prime minister's resignation was a bolt from the blue.

It was a real bolt from the blue when I bumped into my first ever boyfriend in the supermarket.

The announcement about redundancies was a bolt from the blue for the workers in the office.

请注意

另一个短语 out of blue 含义相似 ，也有突如其来，意想不到的意思。

His marriage proposal came out of the blue – but she said yes!