Use 'out of the blue' to express surprise about unpredicted information or events. He dropped out of college out of the blue; nobody saw it coming.
Pro Tip 2/3
Dramatic Impact
The phrase adds drama to a story, emphasizing the shock or surprise element. Out of the blue, a stranger handed her a mysterious package.
Pro Tip 3/3
No Prior Indication
Indicates something happened without any signs or warnings that it was going to happen. The company was thriving, but the CEO's resignation came out of the blue.