I was playing the Byzantines, conquering the Russians, subjegating the Almohads etc. Suddenly, my emperor died with a 10 year old heir and I lose due to lack of heirs. However, that's not why I posted this. It pissed me off that that happened so I reloaded autosave. Then I got a civil war(I sided with 9 star John and 7 star Stephan Commenus, formerly of the royal line vs everyone else). I didn't want to reconquer Russia from 2 providenced so I reloaded again, civil war, but this time Stephan died before and I sided iwth John so... I reload again and then both John and Stephan died before so I lose. But then, I reload one more time and when Emperor Constantine IX dies, I get a King John in Naples and my 10 year old heir was gone.

There are two possibilities: A general married to a princess OR the heir was rushed to the throne.

I don't know what happened so I reloaded and my emperor survives for 20 more years.

So where did King John come from and why was he in Naples? The capitol was in Constantinople still.