Copy from Wowwiki, article about Calia Menethil:
The release of the RPG Horde Player's Guide may have shed some new light on this story. In one of many short stories, a paladin by the name of Andarin tries to infiltrate the Undercity to free prisoners. To his shame, he is quickly discovered by a fallen priest named Trevor. The undead makes him 'an offer he can't refuse': in return for helping Andarin, Andarin must help Trevor free some of the Argent Dawn's prisoners. The paladin ponders the situation but finally agrees, and together they descend into the city. After fighting guards and abominations, the strange duo decides fighting the prison guards will not work and come up with a plan: Andarin will distract the guards and Trevor will free the prisoners. Knowing he has no other choice, the paladin agrees. Trevor quickly manages to get ahold of a keyring and opens the door of a cell in which a girl was locked up. The girl recognizes the Forsaken and is shocked at his appearance, but Trevor simply bows, saying "Good evening, my princess." Given the statement and his standing before becoming one of the Forsaken, it is possible he is showing deference to Princess Calia.