He knew she wasn't Darcia but Diana?.
Darcia informed Ember that she wasn't of this world and Ember explained to her everything.
"I know it's confusing to you, but you've always been a part of this world since the beginning of time. We were all there with you when you were poisoned. But don't blame it on Karl, it was meant to happen in order for you to return back to your original world, which is right here. You should go meet her, she's the only one who can explain it to you".
"What?!. That bastard Karl was meant to happen to me?. But wait…. You all have been with me since?!. Even when I was in my world, including when I was a baby!?. Don't tell me that you all always see my body when I take my bath!?".
"I think so. Should I call the others?. Maybe one of us saw you".