It seems the lore in Warcraft RPG: Shadow and Light was retconned. The Nether Dragons were not related to dragons of Azeroth. However, the new lore of the Outland flying mounts reveals them to be the offspring of Deathwing. Back in the Second War, in Warcraft 2: Beyond the Dark Portal, Deathwing was in Outland. The Alliance Expedition force defeated him, but he escaped through the Dark portal shortly after. Some eggs of Deathwing’s black dragonflight remained behind at the moment Draenor came apart. The energies unleashed by the collapse of Draenor changed the eggs.
One of the most exciting new features of World of Warcraft: The Burning Crusade will be the introduction of a new kind of mount that will provide players with unprecedented freedom to explore the world of Outland from an entirely new perspective. After reaching level 70, players will eventually be able to obtain flying mounts for their characters. The nether drake is one of these.
Read more about the flying mounts of World of Warcraft: The Burning Crusade on our new information page about the nether drake, and also make sure to watch the new nether drake trailer!