They duel before dawn in full power armor. It's only once Albert is defeated and the Count has gotten out to land the killing blow that we realize it's not Albert in the suit.
Franz has drugged Albert and taken his place. Being defeated is all part of the plan.
He has learned Gankutsuou's weakness. It replaces the body of its host with crystalline structure. If there's any man left inside the Count, the heart will be the weak point, and Franz has a conventional sword inside the armor to strike when the Count is close enough.