You should start considering that as canon , seriously when you accept that everything starts to make sense . Jon is a targ , it just doesn't mean that being one makes you immune to fire , but he also has warg powers thanks to his stark blood . IIRC in the books he has dreams about being in ghost so does robb . Martin has said that all the stark children are wargs .
Jon has got both fire and ice , he is the hero of the song of ice and fire and anybody who doesn't accept this is not seeing some of the most obvious clues in the story
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No way , the only reason why they deviate from the story it's because it's better for the restrictions of TV , or because they think the story would be better that way (in the second case they have failed pretty badly) . No reason why they should care about martin imho . If martins solution is the best and they don't think they can come up with anything better (which I doubt they can seeing the results of season 5) they won't do it . Martin resigned in closing his story when he signed the series deal which is a shame , but he has only himself to blame for that .