Responses
Probably because she didn't inherit the black hair and red eyes which is the trademark for being a Castiello.
I think the mother of her brother is a special kind where she could conceive with a cused Castiello blood wherein Estelle's mother is a special case because she were able to conceive a child with a Castiello that is normally unlikely to happen.
This comics take on genetics is baffling. How can you only be half castello? By that logic ur older brother is also only half because you share the same father. Unless the mom was the dads cousin or something Estelle and her brother would have the same amount of Castello d.n.a. from daddio there. I get that maybe the curse is gonna give her leeway cuz technically she's not a legal child, she was born out of wedlock. But. Thats not how genetics work lmao. You get half ur d.n.a. from each parent. Technically both her and her bro are "half castello"