How to fight Aldia in 5 Easy steps
MAKE SURE YOU KILL VENDRICK BEFORE NASHANDRA! Or else use a bonfire ascetic at the kings door bonfire but youll have to face all the throne of want bosses.

1-He will spawn at the Fourth Primal Bonfire you have lit or will light, then exhaust his dialogue then he dissappears
2-Then he will spawn at the First Bonfire at Undead Crypt then talk to him until he asks a yes or no question (answer doesnt matter) then he will dissappear.
3-Next he will appear at Dragon Shrine Bonfire as a smaller version of himself, he will also ask a yes or no question that your answer doesnt matter.
4-Finally he will be at the Throne of want after the Throne Defender/Watcher and Nashandra.
5-He is weaker to Magic and Lightning and has a high resistance to Dark and Fire

Also when he gets to half health he will erect huge pillars of flames around himself causing damage to anyone who gets close.
After the boss fight you can either choose the normal path and go into the throne or you can leave the throne via shining light at the entrance.