Red death titan dies and then the Arbiter is broken by a big red soul.
Made sense that it was Argus, especially since the Dread Lords have been pulling the strings of the Legion the entire time towards Zovaal's goals and they were still putting on an act while we were attacking the Legion on Argus.
I'm just waiting for the ass pull when Zovaal loses and Sargeras gets free saying that he knew the whole time and it was all part of his plan, even losing earlier so he could be in this position later on to be even more powerful. Kinda like Diablo did.