Gladio somehow discovers Noctis secretly enjoys wearing lacy lingerie beneath his regular clothes, and he goes wild for it.

Bonus:
+ Gladio wrecks Noctis while the prince wears the panties
++ Perhaps Prompto and Ignis are nearby, so Gladio and Noctis have to be quiet
+++ Praise kink, Noctis is getting off from how Gladio whispers compliments against his ear about how great he looks in the lingerie

please and thank you!