To let the cat out of the bag

John: I was trying to keep it a surprise, but I accidentally let the cat out of the bag.

Alice: Oh no! I was really looking forward to the surprise. Well, at least now we know!

John: I know, I feel bad. I should have been more careful.

Alice: It's okay. Let's just hope it doesn't ruin everything. It's important to learn from this. Next time, we must ensure not to let the cat out of the bag so early.