Just saw him inside the arena. Right side as you go up the ramp just past the ramp (same side of the arena as the picture above shows, but inside the arena). Standing nose to Adjutant Derkan.
For safety reasons, be sure to kill the giants that roam the area prior to engaging the named. The giants do not seem to add when named is pulled. Straight fight. Mob resists well to spells. Maybe he is a belly caster, but we did not need to get that close to kill him.