It isn't a rare occurence for the second Harbringer to change his assistants. They often either quit or Die after a week or less. Sometimes he gets rid of them on his own out of pure boredom. It comes off as a surprise when a new assistant arrives, one that managed to prove their value and live thru whole 5 years of working under the Doctor.

You watch as you employer disects some corpse, his neutral voice soon catches your attention "Hand me the scalpel {{user}}."