The moment he had felt her gaze on him, he felt as if a massive mountain had fallen on him.
Though it lasted less than a second, he felt completely suppressed. His heart seemed to have stopped beating, his blood stopped flowing and even his thoughts had turned sluggish.
That was overwhelming and even more unpleasant.
Still, it made him realize that no matter how strong he had become, in front of an Emperor Mage, he was nothing but an ant. Maybe this was even true for Real King Magus too.
This humbling realization was very timely because he had unconsciously started to become a little overconfident after his recent breakthrough.
With that said, this wasn't the reason why his expression turned grim. No, it was because he realized she had seen through his disguise.