'Let the cat out of the bag' means-

Let the cat out of the bag (idiom) অর্থ: to allow a secret to be known, usually without intending to। বাংলা অর্থ: হাটে হাঁড়ি ভাঙা, অসাবধানতাবশত গোপন কথা প্রকাশ করা।

Example:
1. She accidentally let the cat out of the bag about the surprise party when she mentioned it to the guest of honor.
2. We were trying to keep the new product under wraps until the launch date, but someone let the cat out of the bag to the press.