He's not Nine, Eleven flat out tells Clara that he is the Eleventh and we see a double in Nine's jacket in one of Clara's scenes.

If anything, he's either very late Eight, when the Time War has gone all to hell, though there's the unkillable theory that he's "technically" the ninth regeneration, coming between Eight and Nine, and scratched from the memory because the Doctor (From Nine on) hated what he became.