This quest was marked obsolete by Blizzard and cannot be obtained or completed.
Slay Lathoric the Black and Obsidion, and return to Thorius in Ironforge with the Head of Lathoric the Black and the Heart of Obsidion.
This... this cannot be. My own brother? He set this all up?
<Thorius' face contorts in anger.>
He betrayed me, he betrayed Ironforge! It seems as if the influence of the Old Gods is still strong in these lands. I fear that if my brother - a once noble and honorable man - was so easily turned to the will of Ragnaros, no one is safe.