I accidentally killed him with a diamond sword (he disappeared like you would expect), so I went to go look for some more rabbits to tame. When I came home, I found Charles hopping about like normal.

He wouldn't TP to me, I couldn't attach a lead to him, I couldn't harm him at all: not even with lava, I couldn't feed him or rename him either.

I went back to the title screen and came back, he was gone. R.I.P