Oh come on. I posted about this not more than two weeks ago. Jaime and Cersei were born 3 years after the wedding, so their birth had nothing to do with the "liberties" that Aerys took with Joanna. Further, Joanna was in CR for a full year before their birth, while Aerys was in KL that whole time. Ergo he cannot be their biological father. Tyrion on the other hand was born 8 1/2 months after the 10-year coronation anniversary tournament where Joanna attended. She was packed back off to CR in cloudy circumstances and Tywin tried to resign as hand at the same time. Gee, I wonder what happened there?
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Tyrion is most certainly a Targ. The whole Dragons being awoken from stone theory has a foundation of sand, though. I sincerely doubt it happens. Imagery suggests that Viserion would have been Tyrion's dragon, had Vis survived.