That Jamie will be the valonqar. Such a turn undoes his arc in Feast of separating himself from Cersei. Also he's her twin, the fact she was born minutes before doesn't matter, age differences are counted by years. Furthermore, the dream Jamie has where Tywin, Cersei, and then him all appear and implied to be dead (don't remember the exact paragraph, it's been years since I've read the books), "the light goes out so must you." This does imply he will outlive his sister.
If anyone in the kingsguard is going to kill Cersei, my money is on Loras.
Aldarion reacted to a post in a topic:
Your Most Hated ASOIAF theory