According to Game of Thrones director Alan Taylor in his chat with Mashable, however, George R. R. Martin was clear to the folks at the show that Dany and Jon were the ultimate players in the game.
Young Griff/Aegon appeared in the Tyrion chapters of fifth (and latest) book in George R. R. Martin’s saga, called A Dance with Dragons.
No need to introduce Aegon if Dany and Jon are the ones who will matter!
It was never confirmed that the young man was truly a Targaryen, but he clearly believed that he was.