Where is the key to the Chest of the Source King?

I just defeated Braccus Rex, but I can't find the key to the magically locked chest in his room. I've read that I can use an unlock scroll to open it, but I'd rather find the key. Where can I get it?

Solution 1:

In the third act/map/whatever of the game, completing the quest "A Forge of Souls" in one manner (dunno if doing it the other way will work) will give you the key.

I don't recall exactly when I got the key, but it was in the process of killing Cassandra (either she drops it or you get it from the "Temple of the Dead")

Though at that point the loot from the chest is useless.

Solution 2:

The purple padlock symbol indicates a magical lock, rather than a mechanical lock. Magical locks cannot be unlocked by mechanical means, such as keys or lockpicks. The only way to unlock them is with magic, specifically the Unlock Magic spell or scroll (Witchcraft).

With a bit of luck you can craft one of these scrolls from a blank Witchcraft scroll, or learn the matching spell if you can find a spellbook. Or try to find/buy one.