Warning: This post contains spoilers from season six of Game of Thrones.
The season six finale of Game of Thrones seemed to confirm at least part of the R+L=J theory, that Jon Snow's parents were actually Rhaegar Targaryen and Lyanna Stark. When Bran time travels back to the Tower of Joy, he sees Lyanna dying in a bed covered in blood and Ned receiving a baby into his arms while Lyanna urges him to promise her...something we can't quite make out.
While the L part of R+L=J was fairly clear from that scene, some fans have speculated whether the R really stood for Rhaegar, or if some other man (perhaps Robert Baratheon) fathered Jon Snow. But in this infographic, which can be seen here at HBO-owned site Making Game of Thrones seems to confirm the theory was right after all.
"The only daughter of Rickard Stark, Lord of Winterfell, Lyanna Stark was engaged to marry Robert Baratheon," the post says. "According to Littlefinger, eyebrows were raised at a tourney hosted at Harrenhal when Prince Rhaegar Targaryen rode past his own wife, Princess Elia Martel, and presented his winner's crown of winter roses to Lyanna instead. Sometime after, news spread that Rhaegar had abducted Lyanna. When her brother Ned made his way to Dorne and found the Tower of Joy, he discovered his sister, Lyanna, drenched in blood and sweat on a bed."
The subsequent infographic shows how key players were related to each other at the time of the Tower of Joy incident, with "parent" lines connecting Rhaegar and Lyanna to Jon, and an "abducted" line connecting Rhaegar to Lyanna. Of course, it's possible HBO is throwing out incorrect information—after all, fans were told for months that Jon was really and truly dead for good before he was resurrected—but it's unclear what would be gained if this were a fib.
Now all that remains in season seven or eight is for Jon to learn of his parentage himself.