I really hope that it's a "The child (hero) is fated to kill him (evil) some day" kind of thing, since that kind of fate can (usually) be changed, especially since he's not originaly from this world and as such would be an anomaly in the fate structure.So he will be %100 picked as the hero and fuck the saintess as is tradition and everyones plans along side it. There are a lot of good ways to handle the asshole gods "he will kill the father" shit as well so its not necceserily bound to end up in tragedy.