From the journal of Jedi Master Arlo Grennen during his investigation into the dark side's influence on Yavin 4:
“There was a time when Freedon Nadd was only known as an impetuous Padawan who murdered his well-regarded master and then fled to parts unknown. But we now know that Nadd fled here, to Yavin 4, thirsty for insight into the dark side. Even now I can feel the corrupting power he must have felt in the halls of these temples. Nadd's arrival reawakened Naga Sadow, who took Nadd as his apprentice. When Nadd emerged from his training, he destroyed Sadow and took his place as Dark Lord of the Sith.
“As far as we're aware, Freedon Nadd never physically returned to the halls of Naga Sadow's temples, but he wasn't entirely finished with the place either. Centuries after his own demise, he would influence another Jedi in training to repeat Yavin 4's dark cycle….”