bolt (from|out of) the blue

news or an event that causes a great surprise

The idiom "bolt from the blue" is used to refer to a sudden, unexpected event or news that takes people by surprise. This expression is originated from the imagery of a clear, blue sky suddenly being disrupted by an unforeseen bolt of lightning. Here are five example sentences

The announcement of his resignation came as a bolt from the blue; no one had any inkling that he was planning to leave.
Winning the lottery was like a bolt from the blue for the struggling family, completely transforming their lives.
Her sudden illness was a bolt from the blue, as she had always been healthy and active.
The company's decision to downsize and lay off employees was a bolt from the blue for the dedicated staff.
Hearing that he had been selected for the prestigious award was a bolt out of the blue, leaving him overwhelmed with gratitude.