Flame angel demise

[AMW]

I have had a flame angel in my mixed-reef tank for several years now. It has always been healthy and mildly aggressive...well, that is until this evening. This morning it was eating and active as usual. This evening I found it dead, floating up against the overflow.
I inspected the dead fish: It appeared well fed, the eyes were clear, there was no obvious legions, trauma, bruises, white spots, ich, etc. All parameters are status quo.
Any thoughts about what may have caused its demise?
Could it have just died of old age? (wishful thinking)

 

[RBU1]

Anything is possible. If all the other fish are acting like normal and your water parameters test ok then I would chalk it up to old age. So many things can happen you will never know. If it is some kind of parasite you should see it surface on the other fish sooner or later. But hopefully just old age...