Prompto had found out because Ignis had taken the time to tell him, in exchange for confirming the first two phases of the prophecy. He wasn't sure if Noct had known or not and the confirmation settles thickly in his stomach, like he swallowed lead, something he wouldn't have cared to do in the first place.

Noctis knew. Noctis hadn't told him.

He could guess why, and mainly it had to do with the fact he was sitting on the floor falling to pieces over the fact that his best friend was going to die and leave him and the loss that they prayed was temporary would be, but the next loss would be anything but.

He choked back a sob, and peered around his hands at Noct, he looked sad, or disappointed. Some combination of the two. He hadn't wanted Prompto to know, but wasn't he going to find out in the end?

He offered him a mournful expression instead of words because he didn't have them.