Did my cats nipple just fall off....

So i was just petting my 15 year old male cats belly, and felt something hard in his fur. I tried to comb aside his fur to see what it was and saw this little papule near where his nipple would be and it just detached as soon as I touched it again. It's really small and hard but the closup definitely makes it seem fleshy. I can definitely see and palate where his other nipple is but can't feel it anymore on this side.

I mean it didn't seem to hurt him at all and he's acting fine and normal now, but that was a total wtf moment and I'm just real curious. Sorry for the weird post and slightly icky photo lol