Littlefinger convinced Joffrey to kill Ned
I have always felt this as well.
I'm convinced it is going to be the key to turning Sansa against him and his ultimate downfall.
The question is, how does Sansa find out??
The obvious answer is The Hound. His feelings for Sansa give him motivation, although it's unclear how his feelings/personality will have changes as Gravedigger. Also, he was ALWAYS around Joff, so he likely would have been in position to hear any conversation where LF was planting the seed in Joff's ear that killing Ned was the kingly move and listening to Cersei and sending him to The Wall would be weak and womanly.
It's a classic LF move. The question is, how does The Hound find her and get her the info. Once LF reveals her as the heir to Winterfell, it will only be a matter of time.
But I've considered recently another possibility. Ser Ilyn Payne could also have been the one to overhear the conversation.
There were several encounters with Payne and Sansa, and it would be fitting if the man she was so frightened of was actually the key to showing her LFs true colors.
I've always felt like there is some greater purpose for Jaime and Ser Ilyn interacting the way they are. Once Jaime finishes his business with UnCat, he will somehow end up getting some sort of info from Payne that he witnessed in KL, and that could be it.
Would be another way to honor his oath to Catelyn, if he can reveal LFs true colors to Sansa in the end.
This post was edited on 11/19 at 6:58 am