Alternative translation:
Maou: Ha ha ha! Hero! I've been watching everything you've all done up to now!
Hero: What?!
Maou: But...
Maou: What the fuck was with last night? Priestess-chan was waiting for you in new lingerie!
Maou: Keep your denseness in check, idiot!
Hero: What are you talking about?!
Priestess: Tell him, Maou-sama!!!