
I'm still curious, i know the test said that they are related but the duke strongly said that he never had sex before so how come she exist? And they said that the previous duke might have had her before he died, so which is which I'm confused and curious

spoiler.....(do not open if you dont want to be spoiled)
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The duke is the father and also the one who made MC reborn. In the past life he found out about his daughter after she had died. So that's why in order to give his daughter a happy life he used his sword which have the power to turn back time to bring back our MC. But he had to pay a price and that was his memories of his beloved wife.
that is why he does not remember being intimate with any woman.

you can find the Korean version in Kakaopage.
https://page.kakao.com/home/내가-딸이에요?/53446232
As I dont speak Korean I actually found the novel spoilers on Novel Updates.
https://forum.novelupdates.com/threads/am-i-the-daughter.114051/
Im crying my single ass out for them