Originally Posted by Spider-Aziz
XM: DOFP will involve early days team and modern day team, if you care to go by fourth in sequence to come starting with 1, in a way it counts
Yeah and you just have to see it in a chronological order.
X1. X-Men (the original cast movie #1)
X2. X2: X-Men United (the original cast movie #2)
X3. X-Men: The Last Stand (the original cast movie #3)
X4. X-Men: Days of Future Past (the original cast movie #4)
Then there's the prequels/spin-offs which didn't feature the majority of the original cast. The general audience didn't see them as X-Men 4.
And since the modern day X-Men will likely go to the past and the movie might end in an altered future with the modern day X-Men. The movie is gonna look like its X-Men 4 more than First Class 2. Anyway, we can only confirm when we saw the movie.
And maybe Bryan Singer said that DOFP is a stand-alone sequel but it doesn't mean it can't be X-Men 4.