Game of Thrones is about to return for its eighth and final season, and theories about how it will all pan out are coming thick and fast. There's a lot for HBO to wrap up in only six episodes (even six extra-long episodes that feel like movies) - from the battle with the White Walkers at Winterfell to the eventual winner of the Iron Throne.
Beyond the big questions, however, there are plenty of smaller plots to be tied up and fan theories to be answered (or, more annoyingly, left hanging). Game Of Thrones is packed with prophecies and possibilities, and that has led to a huge amount of speculation over the identity of the Valonqar (who will presumably kill Cersei), the return of Azor Ahai, and - of course - who might be a secret Targaryen.
In the season 7 finale, it was revealed that there's at least one unrecognized Targaryen running around Westeros: Jon Snow, who is actually the trueborn son of Rhaegar Targaryen and Lyanna Stark. However, some fans have theorized that he's not the only one, and that Jon also has a twin sister who has yet to recognize her own heritage.
Aegon "Jon" Targaryen, Explained
A quick refresher, for those still not clear on how the Bastard of Winterfell could actually be the true heir to the Iron Throne. The big reveal comes courtesy of the Three-Eyed Raven, and starts with the battle at the Tower of Joy, after Robert Baratheon first won the throne from the Mad King. Through Bran Stark, viewers saw Ned Stark and a handful of men fight two of the Kingsguard at the foot of the Tower, believing that they were there to rescue the kidnapped Lyanna Stark. However, when Ned won through to the tower, he found Lyanna dying, having just given birth. She gave a baby to Ned, and whispered to him that the child's name was Aegon Targaryen. Ned then took the child home to be raised as his own bastard, and kept safe at Winterfell.
Season 7 also revealed that Sam Tarly (with more than a little help from Gilly) discovered an important entry in the diary of High Septon Maynard - one that confirmed he had annulled the marriage of Rhaegar and Elia Martell, and married Rhaegar to Lyanna Stark. This makes Jon the true heir to the throne, and not a bastard at all.
The Theory: Jon Has A Twin - Meera Reed
If one fan theory is to be believed, Jon is not only not a bastard - he's not an only child, either. First put forward by Redditor MikeTysonsLifeCoach, this theory posits that Lyanna Stark actually had twins that day, and that while her son was given to Ned and raised as Jon Snow, she also had a daughter, given to Howland Reed and raised as Meera. There's a fair bit of evidence to back this theory, too - although it may seem far-fetched at first glance.
Not a lot is known about Meera (at least, in comparison to Jon), but both were born the same year (283 AC), and while Meera was raised as the trueborn daughter of Howland Reed, her mother is a mystery and goes unmentioned in Game Of Thrones. Meera also looks very similar to Jon (both her description in the books and in the show), with the same pale skin and curly black hair. She's also described in a similar way to Arya and Lyanna in the books, which could back up some blood relation. Of course, her eye color doesn't match that of Jon or the traditional Targaryen violet; however, the crannogmen are known for having some command of magic, especially when it comes to disguises. It's very possible that Howland would have used this to change distinctive purple eyes in order to keep his adopted daughter safe.
As to why Howland Reed would go to all that trouble in order to save an orphaned Targaryen baby? That starts well before the Tower of Joy, and before Robert's Rebellion, with the Tourney At Harrenhal. This massive tourney took place just before the Rebellion, and was where Rhaegar and Lyanna fell for each other. When Lyanna wasn't busy weeping over the beauty of Rhaegar's voice or being crowned Queen of Love and Beauty, though, she was defending the honor of Howland Reed. According to tales of the Tourney, Lyanna came upon Howland being tormented by a trio of squires, and chased them off, inviting Howland to sit with the Starks that night. The next day, a mystery Knight appeared in the lists, bested the squires' knights, and demanded that they punish the squires for their treatment of Howland Reed. No one knew who this mystery Knight was, but it is assumed to be Lyanna herself. If this tale is true, Howland Reed owes Lyanna a huge debt - and taking in her daughter would fulfill that.
Howland, like Ned, would also likely want to protect the infants, because although they supported Robert in his rebellion, they were sickened by the treatment of Elia Martell and her children. Both good men, neither would want to see more infants killed just because they had Targaryen blood - especially not if they also had Stark blood in their veins. So, rather than reveal the Targaryen twins and allow them to die, Howland and Ned made a pact to keep the children safe (which would be easier if they were separated), and never speak of it again.