Angel-like prestige-class

[Rhuark]

Around 3-4 years ago I heard about a particular prestige-class. It is sort of an angel. To become it a character must start as a lawful good cleric or palladin. One of the main prerequisites is to drink water from the river Styx, which then burns out the character's soul and changes him to good outsider (at least partially) or something like that. The bonuses are wings and ability to fly, ability to create a magic sword (+6 or +5) showing up in the character's hand on will etc.
Did anyone hear about that prestige-class? What is the name of that class and where could I find the full description?

 

[VanRichten]

As far as I can tell the closest I ever heard of was in a dragon magazine. And it didn't mention anything about drinking from the river Styx. Though I can't imagine drinking its waters since it flows through the Lower Planes.