What happened at Assassin's Creed Brotherhood at the end?

At the end of the game, Desmond picks up the apple and minerva takes Desmond over, forcing him to stab lucy. My best guess as to why is that Lucy is not eve, so minerva doesn't want her to get in the way of the overall "plan" as only Eve is supposed to accompany him. Minerva saw lucy as a threat because desmond has a thing for her. It isnt said weather or not lucy dies, as that is the point where the game ends. Also, yes there is going to be a 4th one and it is supposed to be called "assasin's creed the merchant of venice". It is set to come out in November of 2011. I'm sure it will continue right where they left off.

Not a big fan of that game but i would say somebody probably dies and another boring game takes a twisted turn and leads you to assasinscreed3

sorry :( no spoilers!!