When fighting kil'jaeden in the sunwell Kalec (formally the first boss) aids you. Whilst helping he tries to waken Anveena, the blood elf that is only one that has the powers to cleanse the sunwell. After may tries it seems that anveena is lost forever until Kalec says:
Kalec: Anveena I love you focus on my voice come back to me now. Only you can cleanse the sunwell.
Anveena finally hears Kalec's cries and replies with:
Anveena: Kalec Is that you?
Kalec: Yes Anveena let faith embrace you now!
At that moment Anveena wakes up and begins channeling a spell. What she has not told Kalec that doing this will take her life forever. After finishing channeling the spell she say:
Anveena: The nightmare is over, the spell is broken. Goodbye my love
Kalec: No Anveena it doesn't have to be like this. Anveena stay with me.
Anveena then dies but by cleansing the sunwell Kil'jaeden is dramatically weakened
Kil'jaeden: The powers of the sunwell turn against me. What have you done, what have you done?
Kalec: I have channeled all i can, the power is in your hands. Strike now hero's while he is weak. Vanquish the deceiver!
Eventually he will die. If you look at Kalec you will see him falls to his knees and cry
Kalec: Anveena I... I love you. I will never forget you. Hero's spread the word to all the world, tell them of Anveena so she may live on. Thank you hero's.
Anveena then starts to glow and disappears, as dose Kalec. They are never to be seen again (unless of coarse you do the instance again).
I wrote this myself. I am still to find a reason why i wrote but anyway hope you enjoyed finding out what happens.
Link to a vid of Kil'jaeden fight WarcraftMovies.com - World of Warcraft Movies