In the caves beneath Niuzao Temple lurks an ancient watcher, apparently from the same Titan brand as Archavon. His name is Huggalon the Heart Watcher. He looks just like the Wrath-era raid boss, if you ignore the giant purple bow on his head. And you should.

To find him, enter the caves on the west side of the island. Take the first right and follow the right-hand walls. Just before you pass through an entrance lit by glowing beetles, you'll see a small passage up and to the right. At the end of this passage, Huggalon waits. You won't see a rare icon on your map because he is not a rare spawn.