Sebille Personal Quest - Hunting the Master

[Drynn]

Hi Stuck and could use a little help here is what ive done so far:

Killed roost and rescued the elf being help captive
They told me I was the prime scion and sent me on a mission too find the mother tree
Found the Mother tree on nameless isle she gave me a quest too kill a demon

Thats about as much as I have done The quest told me the master was on the nameless isle and I cannot seem too find him. Also I cannot find the void tree in stonegarden the one who tells me the mother is bad and has imprisoned the elves anyone have any insight or know what I have too do next?

[Captain BlackFace]

the shadow prince is in the southwest of the map, near the temple of Zorl-Stissa