Tertius is a Iron Knight that was based off of Ash, the youngest Winter prince. Like all Iron Knights, he is unswervingly loyal to whoever sits on the Iron throne. He was killed by Puck in The Iron Queen when Puck, along with Meghan and Ash, broke into Ferrum's castle to try and kill Ferrum to stop the war between Winter/Summer and Iron. He aslo killed Sage and his wolf. Sorry for lack of info. I will read up and add more.