Most people accept the popular Jon Snow theory that states that Jon's real parents are Rhaegar Targaryen (Daenerys' older brother, who died before the events of season 1) and Lyanna Stark (Ned Stark's dead sister).
The theory goes that Rhaegar impregnated Lyanna, then hid her in a place called the Tower of Joy. Ned and his good friend Howland Reed then stormed the Tower of Joy and rescued Lyanna, who died then and there in childbirth.
However, with her dying breath, Lyanna made Ned promise to keep her baby, Jon Snow, safe from harm. After all, Ned knew that Robert Baratheon wanted all Targaryen's dead, and Jon is half Targaryen according to this theory.
But what if I told you that this wasn't the whole truth? What if there was another theory that might just change everything we thought we knew about everyone's favorite bastard? Maybe, like Jon Snow, we all know nothing.
First of all, we know that a young Ned Stark has been cast for a flashback in Season 6.
Some fans suggested that the flashback could feature Ned Stark and his sister Lyanna, and that the scene would show Lyanna making Ned promise to keep Jon safe.
But one fan in particular took things even further - what if THIS is how the scene happens:
[Ned holds the newborn Jon Snow in his arms.] The dialogue swells and clarifies to [Lyanna's] voice, "Promise me, Ned." Her eyes slowly close. Ned begins to sob. He raises his head to the sound of another high pitch noise coming from the foot of the bed. A baby girl.
That's right - what if Jon Snow has a twin sister?
At first, this might make no sense. Where did this other twin end up? Who is Jon Snow's twin? Is it a character we already know? What evidence is there for this madness?
The thing to remember is that when Ned Stark went to the Tower of Joy to retrieve his sister Lyanna, he wasn't alone. Howland Reed, father of Meera and Jojen Reed was with him. Maybe you've already guessed what I'm going to say?
Meera Reed is Jon Snow's secret twin sister!
If Lyanna had twins, then the safest plan for keeping them safe would be to split them up. The son went with Eddard and became Jon Snow, and the daughter went with Howland and became Meera Reed, who now travels with Bran.
Jon and Meera look extremely similar, which could have been a conscious casting decision by the producers.
According to 'A Wiki of Ice and Fire, and the appendix of the second novel. Meera and Jon are the exact same age - 15. The wiki lists Meera and Jon's birth year as 283 AC, the same year as Lyanna's death.
We already know that George RR Martin likes to pull inspiration from real life history and mythology. The Red Wedding, for example, was inspired by a similarly gruesome mealtime massacre that occurred in Scotland.
And it just so happens that there is a real life historical occurrence that supports this crazy Jon Snow theory - the story of Romulus and Remus in the myth of Rome's foundation.
The legend is as follows: the king of Alba Longa was usurped by his brother. To keep control of the throne, the new king had to wipe out the old king's bloodline by killing his heirs and forcing the king's daughter, Rhea Silvia, to never have children.
However, Rhea went against his wishes and gave birth to twins - Romulus and Remus. The twins then had to escape the king's grasp, just like Jon Snow and Meera Reed had to be hidden and kept secret too.
But the connections get even weirder:
-The twins in the myth grew up unaware of their true identities. Just like Jon and Meera, who grew up with different families.
-The mother of the twins is named Rhea. Now look at the name of Jon and Meera's alleged father: Rhaegar Targaryen. Extremely similar first names.
-The king who wanted to wipe out the old king's bloodline is similar to Robert Baratheon and his desire to wipe out all the Targaryen children (which would include Jon and Meera since they're half Targaryen).
-And last, but not least. Guess how the twins in this story escaped the evil king's grasp? By getting carried away and nursed by a powerful she-wolf. The Stark symbolism here is obvious. The twins were saved by a WOLF, just like the twins in Thrones have been saved by the STARKS (the dire wolves).