"You have birthmark," Iris stated when she came closer to see Zale's birthmark because the shape of it was pretty interesting. She saw this shape before and was curious how he could get the same exact shape of the Holy Knight's crest.
No, she saw this crest inside that hut too…
The mark was right on the middle of his shoulder blades, so unless you saw it yourself on the mirror or someone told you, you wouldn't be able to know it was there.
"Am I?" Zale asked, he tried to look over his shoulder, but it didn't work.
"Yes, you have it." Just like Iris thought, he didn't have any idea that it was there. "Here." She pointed at his birthmark and it shone.