According to my research:
Any of the froglok wan knight's in the southern mini castle (Loc 237, -559, -220) can be a PH for this ultra rare named. But the best and most often way to pop him is by killing the wan knights that roam the circular tunnels directly surrounding the mini castle.
Following magelo link shows the path markers for the tunnel.
http://eq.magelo.com/npc/103985