But there are a few quests surrounding the boss as well -- for more on how he might be included in the game during the world event (including possible spoilers), hit the link below.
Apparently the quest to find Tenris come from an Argent Dawn emissary (which haven't yet appeared on the servers as of this writing -- all we've got so far are Argent Dawn healers to try and get that plague off). The emissary tells you that there is a new threat within Karazhan, not from Medivh or the Burning Legion, but from the Scourge itself. He then sends you to the Servants' Quarters (where the animal bosses are, and where most Kara raids don't go much anymore) to find Tenris and see what's going on (read: kill him). The quest gives a trinket called the "Monster Slayer's kit" which looks like it provides a random attack in the form of a monster.
The quest, unlike the actual boss or NPC, is apparently in the game at the moment (as a file, not as a doable quest yet), so there is a ring of truth to all of this, but seeing all these things now is kind of like looking at an unsolved jigsaw puzzle -- there are a lot of colorful pieces in there, but we still can't see the actual picture yet. Stay tuned, though -- our countdown is counting ever closer to Wrath's release, and the world event (which is already awesome) keeps ratcheting up.