When it comes to Star Wars Episode VII: The Force Awakens just about everyone on the internet is convinced that Rey is Luke Skywalker's daughter but one fan is convinced she isn't the exiled Jedi's only child.
They argue that Han and Leia's son Ben isn't actually their son at all, and that uncle Luke is his real father.
Now, we all know that in the original Star Wars expanded universe Han and Leia had twins called Jacen and Jaina – but given the fact that the Force Awakens novel puts Rey at 19 and Kylo Ren closer to 30, there's sadly no way they can be the Solo twins.
However, that doesn't rule out the possibility that they could be siblings, separated much like Luke and Leia before them, who also never knew the other existed.
The theory goes that Luke had a child with a female character we're yet to meet, but decided that as a pretty infamous Jedi he couldn't possibly raise him so he handed him over to Luke and Leia for safekeeping. It's not like the Skywalkers aren't known for offloading their kids on their relatives for the sake of their own safety.
That would also explain why Kylo Ren's real name is Ben. Leia and Han weren't half as close to Obi-Wan as Luke was, and in the original expanded universe it was Luke who chose Ben as the name for his son. The plot, as they say, thickens.
And if Ben Solo was to somehow discover that Luke was his real father he'd be pretty emotional, right? I mean Luke did pretty much lose it when he found out who his daddy was. So that might explain why he has such spectacular daddy issues and a LOT of pent up rage.
"Your son is dead" he tells Han Solo. "He was weak and foolish, like his father". But what if the father he was referring to was a Jedi who wanted to keep Ben on the light side of The Force? It's not exactly a wild theory in the Star Wars universe.
How does Rey fit in then? Well, the theory suggests that Luke went on to have another child, whom he either chose to raise and train (much to Kylo's annoyance) or sent off to Jakku before her increasingly evil brother could ever discover she existed.
As the theorist in question writes:
"Rey is able to fight back against Kylo Ren, and can even sense he is afraid of not being like Darth Vader (Like Leia sensing Luke was in danger). Perhaps when Kylo Ren says “I will finish what you started, grandfather” he means he will succeed in getting the next Skywalker in line to rule the galaxy with him. Where Vader failed in getting Luke to join him, Kylo Ren will succeed in getting Rey to join him, bringing balance to the Force."
It's such a pity that Episode VIII has been pushed back and we're going to have to wait that bit longer to discover the truth.