This was revealed a while back: http://www.gamenguide.com/articles/1540/20120428/skyrim-dlc-snow-elves-prince-mystery-revealed.htm

But there is no Snow Prince in the Dawnguard DLC pack right?

Now what we can see in the Dawnguard that there is this Knight-Paladin guy goes back to the Chantry and says he will stay there due to his oath and mention that maybe some other still uncorrupted Snow Elves will still find their way there too. There is also a dialogue about possible cure and while he says he doesn't believe it's possible to cure them, he suggests that they might slowly be able to change slowly to their former glory somehow.

What do you guys think of it?