this is a reference to Aerys' improper behaviour towards Tywin's wife on their wedding night, yes? Isn't that pretty much invalidated by the detail of Tyrion being the youngest child? Even in the extremely unlikely event that Aerys would've gone as far as to actually rape Tywin's wife without being killed in the process, it still wouldn't be Tyrion whom he might've fathered, but Jaime and Cersei (certainly would explain a few things about Cersei...).