WARNING – This post contains loads of spoilers.

LONDON – If there's one thing Game of Thrones fans enjoy, it's a good theory, and the newest one – which concerns the show's most talked about character as of late, Jon Snow – definitely doesn't disappoint.

This theory is actually a fairly complicated extension of another much talked about fan theory – the R+L=J theory, explained here in 3 minutes – which suggests that Jon Snow is not actually Ned's bastard son at all, but is in fact the son of Rhaegar Targaryen and Lyanna Stark (hence the R+L thing) and therefore the rightful heir to the Iron Throne.

If Jon Snow is actually dead, though – despite all those rumours that were going round about his hair – then that creates a bit of a problem for the R+L=J theory, doesn't it? Because what would be the point in George R.R. Martin creating such a complicated, twisting backstory that finally places Snow as the rightful heir to the Iron Throne only for him to die before he can fulfil his destiny? We know that Martin is cruel beyond all measure, but surely he's not that cruel, is he?

Well, this is where the current fan theory comes in...

Image: Mashable composite/HBO

The new fan theory suggests Jon Snow actually has a twin sister.

In a recent discussion on Reddit, ghostchief predicted that the opening scene of Series 6 would feature a flashback to Ned Stark finding a dying Lyanna in the Tower of Joy. Now, in the original R+L=J theory, theorists have said they believe that this moment – where a dying Lyanna says, "Promise me, Ned" – actually takes place shortly after she's given birth, and what she's really asking Ned to promise her is that he'll take care of her baby (a.k.a. an infant Jon Snow) who is the rightful heir to the throne.

The R+L=J+M theory (we'll come on to the "M" part in a bit) takes this one step further, though; in the predicted opening scene described by ghostchief, a sobbing Ned Stark is distracted from his sister's death by the cries of a baby girl – a baby girl who is Jon Snow's twin sister.

Jon Snow...has a twin?! — Eleutharias Frome (@WallingfordDude) August 26, 2015

People are speculating that Meera Reed is Jon Snow's long-lost twin.

Here's where things get even more crazy. Some people are now combining an old theory – that Meera Reed, the girl currently with Bran, is actually Jon Snow's twin sister – with this other theory about Jon Snow's parentage; hence the R+L=J+M.

Despite the fact that Jon Snow looks a hell of a lot older than Meera in the TV series, this impressively in-depth Wiki of Ice and Fire lists the birth years of both characters as 283 AC – which would make them the same age. When you add in the fact that Lyanna Stark is also listed by the Wiki as dying in 283 AC (and Meera's supposed father Howland Reed was with Ned at the Tower of Joy on the day they went to find Lyanna), it seems like there's more than enough ground for a good old fan theory.

Also, they look sort of similar.

So the latest #GoT theory is that Jon Snow has a twin sister. If you watch the show, who looks a bit like Jon? — Thalin (@Return2Mirkwood) August 28, 2015

So what would it mean if it's true?

Well, good question. Obviously if the theory is true (and before we get too excited let's not forget that the theory is actually a combination of two different theories, both of which could turn out to be completely wrong), it would surely mean that Meera has a much bigger role to play in the series.

Jon Snow has long been rumoured to be a massively important character – and Melisandre seems to think he could be the legendary hero and potential White Walker-conquerer Azor Ahai – but if he's dead, maybe his sister will turn out be the true hero?

how am I supposed to do any work when jon snow might have a twin sister — aerp (@aliii1ce) August 28, 2015

It does all sound sort of far-fetched, but then again this is George R.R. Martin we're dealing with so who really knows what will happen. And, seeing as he's still slowly chugging his way through the next book and it doesn't sound like it'll be coming out any time soon, we might as well keep speculating in the meantime.