(Warning - potential SPOILERS for Deadpool, and the future of the cinematic X-Universe are to be found below...)
Now, if there's one thing you can be pretty much sure of when it comes to Deadpool, it's that things aren't likely to go quite the way anyone's expecting. After all, the Merc with a Mouth is renowned for being both intensely meta, and hugely unreliable. Expect him to kill Character A, and there's just as much chance of him making out with them, dumping them in a ball pool, or killing the entirely unrelated Character F - all the while talking to us about how ridiculous it all is.
Similarly, from what we've seen and heard so far, there're no real guarantees that the character's upcoming solo movie, Deadpool, will have any stronger a grasp on what we know of as reality. So much so, in fact, that it seems worth asking a slightly out-there question:
Is Deadpool Secretly Set in an Alternate Reality?
Specifically, an alternate reality to the one we've thus far seen in the X-Men movies.
It may sound a little strange, but there's actually a pretty solid amount of evidence in its favor. First up?
We Already Know That the X-Men Universe HAS Multiple Realities
After all, as the end of X-Men: Days of Future Past made abundantly clear, the X-Universe is able to incorporate multiple realities - including both the one we saw in the first X-Men movies, and the (increasingly different) one we saw at the end of Days of Future Past. Indeed, the upcoming X-Men: Apocalypse exists in a very different X-Universe to the one we saw in the earlier films, with characters like Angel and Jubilee appearing to have been born far earlier than they previously were.
As a result, it's by no means clear - as it would be in, for instance, the Marvel Cinematic Universe - that Deadpool will neatly slot into the previously existing X-Universe, especially as the movie appears to be set in the present day, in contrast to the past two X-Men movies.
What We've Seen So Far of Deadpool Suggests a Very Different Reality to the One We've Seen Elsewhere
The big problem? From what we've seen so far of the X-Men set to appear in Deadpool, they sure don't seem like the superheroes we know and love from the movies that've gone before.
After all, even though we know that Colossus is set to cameo in the movie, the Deadpool trailer revealed at this year's San Diego Comic-Con seemed to suggest that he's a very different version of the hero to the one we saw in the earlier movies. Now, in terms of re-casting, that's all well and good - albeit a little unusual in the X-Universe - but since his whole appearance, and, notably, his general scale, seem to have changed - it's not too difficult to imagine that this is a very different Colossus to the one we've seen before.
Similarly, Negasonic Teenage Warhead?
She doesn't seem like the most obvious product of any X-Men school we've seen in the movies thus far - especially since the Comic-Con trailer very much makes it seem as though the young character is out on a combat mission, which frankly seems an odd fit with any of the X-Men universes we've so far seen on screen.
And, finally (and crucially):
It Would Explain Why Deadpool Is Being Introduced in His Own Solo Movie...Before X-Men: Apocalypse
After all, if Deadpool does indeed prove to be set in the same basic reality as X-Men: Apocalypse, it seems a little odd that we're about to see the latter's future (Apocalypse being set in the '80s, and Deadpool seemingly in the modern day). After all, if Deadpool is the future of the same reality as X-Men: Apocalypse, we can pretty reliably assume that everything is going to be OK in the end, and not worry too much about Apocalypse's gargantuan existential threats.
All of which means it might actually make the most sense for Deadpool to be set in an alternative reality - one in which he can break the fourth wall to his heart's content, and gleefully comment on the alternate origin story he had back in X-Men Origins: Wolverine.
And then, in a year or two's time, he could presumably somehow cross over into the 'mainstream' X-Men universe, and cause all kinds of havoc...