Read another (seemingly unpopular) theory that it's Jamie and Cersei, rather than Tyrion, who are the bastard children of Joanna Lannister and Aegon Targeryan. Some very interesting parallels:
- Cersei's destruction of the Sept mirroring Aegon's plans for King's Landing, plus her tendency towards torture.
- Outside of these 2, the only other incest in the show is amongst Targeryans; in fact, in the books I believe it's mentioned that the only other man Cersei had been infactuated with was Rhaegar, who would also be her brother (in this theory).
- It is said that when a Targeryan is born, the gods role a dice with the outcome being psychotic death-crazed madman (Cersei) or honourable and dutiful (Jamie - sort of).
- They are older than Tyrion and the Joanna/Aegon thing was meant to have happened on Twyin's wedding night (I believe this was taken from something Ser Barristan had said).
- Been mentioned in the book that Tyrion is more like his father than the twins.
I can't really see it panning out that way, but I dont hate the theory!
Also, the way we are going this season I reckon there'll be more battles with White Walkers than there will be between Cersei/Dany...