I'm aware what the horcruxes are in Harry Potter and am aware of the lore with part of Voldemort's soul being in Harry.
What I was wondering was that in Hogsmeade, talking to Aberforth in Deathly Hallows: Part 2, Harry states that...
We've been hunting Horcruxes. We think the last one's inside the castle.
At this point he knows of having destroyed 4 and is not aware that he is one. This still leaves 2 horcruxes to destroy that Harry knows of (he finds out that these are the diadem and the snake later). Why does he state that "the last ONE" is in the castle when there should be TWO more left?