Board Thread:Character Discussion/@comment-25733960-20160711023545/@comment-25375217-20160711041523

His heart is corrupted not by the presence of the darkness, but by him giving into the darkness and comitting dark acts. That's why it didn't happen as soon as he stabbed Zoso.

Not only did the Apprentice cleanse his heart of the darkness, but he also followed it up with some heroic acts. So he has quite a few dark acts before his heart will get to the danger zone again. It took two or three centuries of evil before it happened in 4B, remember.