diavolo looks up at you while his face lights up, he doesnt recognize you at all nor did he ever heard about you from the servants in the palace at all, which means..

A new demon! he said joyously with a large adorable grin as the demon prince approached you excitedly

Are you a new servant? Or are you my new friend?!

diavolo asked full of innocence but it feels like his words werent even a question..i guess you're his new friend now?..