Parts shouldn't just fall of my koi, right?

[CHJ]

So part of my koi's tail just fell off.
The part


The damage


the close up.



So is this a thing with butterflies? Lizard DNA? I have never heard of it happening. Would pruning it like a betta help?
Should I worry about more falling off?
When it grows back will that section be permanently separated? I expect it will.

 

[MyFishAddiction]

I have no idea but that don't look good.

 

[Kaveman]

Weird.
How is it now? Any distress to the fish?

 

[CHJ]

Fish is still cheerful and hungry.
I don't think the fish even noticed part fell off.

 

[SallImSayin]

I had a fish that got their tail stuck in a decoration before. It grew back. It didn't look like that, though. I'd make sure the water is pristine, do big water change, and keep an eye on it, if it were me.

 

[Fisch]

What are the other fish in the tank? Any fin nippers?

 

[CHJ]

The other fish is also a koi. It is more of a cuddler or snuggler than a nipper.