Although the Sunwell's threat was ended, Kael'thas could not have foreseen the effect its loss would have on his people. The elves suffered terribly from withdrawal, for many of them had been infused with the arcane energies of the well all their lives. Only in the absence of the Sunwell did the blood elves come to realize how addicted they had grown to its powers. Over time the elves grew ill, and the youngest and oldest among them died. Determined to find a cure for his people's crippling addiction, Prince Kael'thas sought a renewed source of arcane power, and he soon fell into the service of the demon Illidan Stormrage.
With Illidan's aid, the blood elves found a temporary reprieve, learning to siphon the magical energies of others to ease their own suffering. As Kael'thas joined the fight against Illidan's many enemies, the prince came to rely more and more on fel energy: the dark and corrupting essence wielded by the demonic Burning Legion itself.
Now, bristling with newfound power, Kael'thas has turned his back on his former master, Illidan, and has finally returned to Quel'Thalas, promising final deliverance to his people. To this end he has harnessed the mortal possessor of the Sunwell's energies, Anveena. Yet many believe that the prince's exposure to fel energies has made him unstable, and that he has sought out a new master, a demon lord of the Burning Legion so terrible that even the mighty Illidan would tremble in fear at the sound of his name:
Kil'jaeden.