Raze your totally right! I forgot about the blue ring boss and used the teleporters to get across the spikes thinking this was just part of the game. How did you know I jumped the spikes lol?
I went back killed the blue ring boss and then the cutscene triggered. I'm going to rename the thread as this wasn't gamebreaking, although still a bug because it let me into his room.
Thanks for the help! I'm thinking I will do a 2nd run with a thief-mage at some point.