Inspired by Episode Ignis trailer and Ardyn's quote in Chapter 13 "So you are the Chosen King...but you are a second choice, at best". The most common interpretation of this line is that Ardyn was talking about himself as first Chosen King, but Bahamut later said Ardyn was rejected by Crystal.
So what if Ignis was the first choice? What if Crystal chose 2 Kings - one is King of Light, born to die, the other King of Insomnia, born to rule? No one knows except Regis, who actually prepared Ignis for this role, while Noctis was sacrifical lamb all this time.
Ignis/Noctis or Gen - Ignis was Chosen King all along
So what if Ignis was the first choice? What if Crystal chose 2 Kings - one is King of Light, born to die, the other King of Insomnia, born to rule? No one knows except Regis, who actually prepared Ignis for this role, while Noctis was sacrifical lamb all this time.