Remember Game of Thrones? If you do, you might remember a character named "Jon Snow."
He's mopey all the time, mostly because he's a bastard - he was conceived out of wedlock, and therefore cannot have his father's surname, Stark. Although NOT having Stark as your last name is usually a good thing, mortality-wise.
Since forever, Jon Snow's wanted to know more about his mother. Who is she? What about her got Ned to break his marital vows? WHY DOESN'T SHE LOVE ME? That kinda thing.
There's a few candidates we can eliminate right away:
Luckily, the fandom around Game of Thrones has already put together enough of the clues left by George Ruff-Rider Martin to come up with a pretty concrete theory. And this helpful Youtuber has put it all into one nicely constructed video: