TheTenthDoctor
Fish Herder
Heres my take. If he was 3 years old he probably died a natural death of old age and go washed up into the guppy grass. Or perhaps poor genetics caused some kind of internal failure that is impossible to detect. He appears to have been taken care of in the best possible way. His tank looks nice, and the water parameters are fine. Just make sure there is no chlorine in your water. Honestly you gave him a good life. There is no reason to feel sad