Dargonax (in Dragonic Devourer), "son" of Sinestra, created from a dragon egg of powers of nether dragons.. Burned away with a brightness of sun. One of the FIRST Twilight dragons.
Would be epic if we could see this as a raid boss (maybe in same raid as Deathwing?). Wouldn't it?
http://www.wowwiki.com/Dargonax