Celestial Steed

The Celestial Steed serves both as a flying and a ground mount depending on the terrain. Freshly born from the Twisting Nether, this supernatural warhorse takes flight with wings of pure elemental stardust.

This mount is directly purchasable from Blizzard. Released on April 15, 2010, it is the first mount to ever be offered in this way.

Source
This item is available for purchase from the shop or the In-Game Store for $25 or €25. It was released on April 15, 2010 along with Lil' XT.

Mount Journal
A beacon of hope; a guiding light in the darkness.

Saddle up the stars on this supernatural flying mount.
 * In-Game Store

Light up the night skies of Azeroth - ''Freshly born from the Twisting Nether, the Celestial Steed flying mount lets you travel in style astride wings of pure elemental stardust. So saddle up, because this supernatural warhorse will fly as fast as your riding skill will take you.''
 * Blizzard Shop

Mail
Players are mailed this mount by :

Named

 * Twinkles