"C’Thun has been wakening for some time. He recently woke completely and physically returned to Azeroth. He now lairs in the ruins of Ahn'Qiraj, and packs of brave heroes have already begun to form and venture into the ruins. At some point during his stewardship of Ulduar, Loken came under the sway of Yogg-Saron imprisoned within and eventually betrayed both the Pantheon and his own brother, Thorim. He resides in Ulduar's Halls of Lightning, seeking to free Yogg-Saron completely. According to Malfurion Stormrage, one of the Old Gods is behind the Nightmare corrupting the Emerald Dream. Although the Nightmare Lord in the dream turned out to be the Satyr Lord Xavius, it is suspected that he acted on behalf of a power even greater and darker than Sargeras. This seems to be confirmed in World of Warcraft: Cataclysm."
Is this already known? As I just found out of this tonight. What is greater and darker than Sargeras in the lore?