So, in conclusion, Ned took his vows very seriously and he promised his sister to keep Jon safe. He endured jeering, mocking and confrontations with his wife but he never put Jon’s security at risk by telling his true identity to anyone. Some things are better left buried. Ned actually thinks about this while he’s confronting Cersei. If Catelyn thought that she could get Sansa and Arya back by handing Jon — a Targaryen heir — to the Lannisters, would she have done it? Most surely yes.
Alright everybody, get ready for this one… This is going to seem farfetched but at least this theory hasn’t been discussed yet so it will give you something to ponder! Before I continue I would like to say that this theory came to me after reading the books and as the books are not with me at work right now nothing is referenced and therefore some details could be off (although this isn’t so much as a line for line theory as a bigger idea right now).