It's true, Gaga liked a video on Instagram with that snippet playing in the background ! It's her actual voice, and the leak is in really high quality, we're probably soon gonna get the full entire song, and I wouldn't be surprised if Gaga was behind the leak lmao... Some people think the lyrics come from Monster but it's really different, and Gaga has already used previous vocals by the past to make new songs (Earthquake -> Fashion Of His Love for instance)

I think it's Fake