Izen was informed about Gabriel by Eliana. According to what she said, Gabriel was most probably using an illusion. However, the illusions were useless to him. Unfortunately, even while ignoring the illusion, he couldn't see much since Gabriel was wearing a mask.
Despite that, he still found Gabriel somewhat familiar. It was as if he had seen the young man before. The body built of Gabriel reminded him a lot of the young man that had escaped from his hand last time. However, he couldn't believe that to be the case. How could it even be possible?
From what he knew, the person that escaped from him was a dark mage. There was no way he could've entered the Church of Light and survived so far, especially with the presence of the Lord of Light inside. At least, that's what his mind was telling him. However, his heart... It was saying otherwise!