the cat is out of the bag
Some secret or surprise has been revealed or exposed. Well, we were going to keep this project a secret until we were a little further along in development, but I guess the cat is out of the bag now. We've had hidden cameras and microphones installed in his apartment to gather incriminating evidence, but I think the cat's out of the bag.
the cat is out of the bag
Fig. the secret has been made known. (See also .) Now that the cat is out of the bag, there is no sense in pretending we don't know what's really happening.