Originally Posted by Ornery Wyvern
Ned and Lord Arryn's theory that Joffrey and his siblings are children of incest rather than of Robert Baratheon is really pretty weak. I believe, and I could be wrong, that we have yet to encounter a Lannister without their trademark golden hair. It seems unlikely that the Lannisters have avoided marrying anyone with dark hair. Given these two things wouldn't Lannister gold need to be a dominant trait, and thus potentially be capable of producing three golden haired kiddiwinks?
I admit that the book and bastards are convincing, but did Lord Arryn really have the gentics knowledge to make such a call? I suppose it was confirmed by the death of Lord Arryn... And perhaps he did have more reason, maybe he caught the Cersei and Jaime show at some point...