Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'm here to help you. I think what you are describing in Prince is his "skirt". . .at least that is what I have always called this. Even some cats that are thin will have this. . .or an overweight cat will get fat tissue layed down here.
The best way for me to tell would be if you can send a picture of this area to me. Two angles would be good. . .one a profile of his body when he is standing, and one with him laying on his back. Would this be possible?