The reason Noctis has such low stamina is because he has chronic pain from the injury he got from the Marilith. No one who knows this has told anyone that actually interacts with the Prince. So when Noctis has a bad day, and misses practice with Gladio or completely blocks out Ignis when he's trying to tell/teach Noctis something, they believe that he is just being a brat.

I want reactions when they find out.

Gladio seems to have issues with respect if someone doesn't fit into the boxes he has for them so I'm not sure how much he's going to care. Or how much he understands of what chronic pain is and why Noct gets away with not practicing on a set schedule.

Gen or any pairing but Ardyn.