Rift Quest:The Heart of the Destroyer  

Enter King's Breach on expert difficulty. Complete the dungeon and in the final room you will find the Vault of Secrets. Use the Key of Secrets in the final room of the dungeon to being the event.

The Heart of Regulos will spawn and summon the Shade of Regulos. This shade is extremely difficult. It has a randomly targeted AoE bolt that can do 8k+ damage. However because the shade is not considered a boss it is affected by crowd controls. So liberal use of interrupts, fears, confuses, or any other CC can make this fight much much easier. This will take a long time but eventually the shade will die and the Heart will start attacking.

When the heart is attacking the group can use the pillars in the room to line of site the boss to avoid any damage. NOTE: you must use the quest item on the Heart BEFORE it dies! Now use the Blade of Light on the Heart and collect the Blade of Life's Death. This will update the quest and now simply finish off the heart to complete the quest.