He married the daughter of the maid, but as stated by the royal family, they believe she's a bastard child of the count because that hair and eye color are rare.
We haven't heard anything about her mother saying she didn't want her daughter to marry the Duke because the mother has been too sick. They've been using the mother's sickness against the illegitimate child in order to keep her in line and to keep up the ruse that she was the original child that was supposed to go there.
But the Duke knew that she wasn't the count's original daughter that he was supposed to marry from the start. And he accepted her because he fell in love the first time they met at their wedding.

Can someone tell me about dukes point of view I think I read a manwha that a northern duke married a maid because of a marquis that wanted to married her daughter to northern duke but then the mother do not want to go her daughter to marry the northern duke because she was afraid hee daughter might die so they send the maid that looks like their daughter or maybe that was illegitimate child I don't know but I think I read something like that I cannot just remember ╥﹏╥