Since Jon Snow's return from the dead on last week's episode of Game of Thrones, fan theories about his significance to Westeros and the overall Game of Thrones story have also taken on new life and sparked much discussion. One of those theories has to do with Jon Snow's true parentage, and the preview for tonight's episode, titled "Oathbreaker" includes a clip that could support this theory. It's called the R+L+J Theory, and if it proves to be true, it changes everything for Jon Snow and a lot of other people.

Ever since the first season of Game of Thrones, viewers have been led to believe that Jon Snow is the bastard son of Ned Stark and an unidentified woman with whom he had an affair. The story we've been told is that when Ned returned from fighting in Robert's rebellion, he returned with an infant, Jon Snow, and told his wife and everyone else at Winterfell that he had been born of his mistress. Game of Thrones fans as well as some GOT characters have expressed disbelief that Ned Stark, a man of great honor, would have an adulterous relationship. It would be a great deviation from the Ned Stark everyone so admired as a man of great virtue who was so loyal to his family. The R+L=J Theory explains how Jon Snow and Ned's explanation about his mother completely align with his integrity. It also says that Jon's birth put the Stark patriarch in quite a dilemma. He had to decide between telling a lie that would put a wedge between him and his wife Catelyn but protect his sister or telling the truth that would avoid the marital conflict but tarnish his sister's legacy.

The theory of R+L=J goes like this. Jon Snow is not the son of Ned Stark and a mistress, but rather is the child of Rhaegar Targaryen and Lyanna Stark. (Rhaegar + Lyanna = Jon). Rhaegar was the older brother of Daenerys. He was betrothed to another but secretly was in love with Lyanna Stark, sister of Ned. Westeros' citizens have been told that he abducted Lyanna and raped her. But this theory of Jon Snow's parentage says that Lyanna was in love with him and went with him quite willingly. Further, Lyanna was pregnant with his child, Jon. Robert's Rebellion began when Rhaegar took Lyanna. Here's where the preview shot comes in.

Jon Snow's father, Ned, fought in a battle of Robert's Rebellion just outside The Tower of Joy in which Rhaegar had placed Lyanna. There is a clip in the preview for this week's episode that appears to be that battle. It appears to be one of Bran's visions and begins about 22 seconds in. One of the men in that shot could very well be Ned Stark, and the building in the background could be The Tower of Joy.

The rest of this theory about the true identity of Jon Snow's parents says that after the battle, Ned hears someone crying in the tower. He goes to the source and finds his sister, Lyanna, bloody. This much is in the Game of Thrones books. What happens next is that she gives her brother a newborn infant, Jon Snow, and makes him swear to take care of him. He does and, in order to protect her legacy and further complications with his friend Robert Baratheon he lies and tells everyone that Jon is his bastard son.

If this is true, it means that Jon Snow is part Targaryen and a legitimate heir to The Iron Throne. If it's true, things will get really interesting when Jon and Daenerys have to deal with this reality. We've heard that Season 6 of Game of Thrones will be the biggest one yet for Jon Snow, and playing out this fan theory would easily make that true.

Game of Thrones airs on HBO on Sunday nights at 9 p.m. ET.

[Photo by Anthony Harvey/Getty Images]