Flesh atronach achiev in Razak's Wheel

Teoulas

There is a group challenge achievement that says kill the flesh atronach in Razak's Wheel, Does anyone know how can you summon this boss? In a room I saw a flesh atronach on a table cleared teh mobs around it and then an imperial mage revived that beast but it wasnt a boss only the imperial was and got no achievement by killing it.