Responses
it was pretty common for relatives to marry back in historical times, they wanted to keep bloodlines strong and as pure as possible so cousins and such would marry often. in fact dukes are branch families to royals so if the prince had married Lady Iris than he's be marrying his relative since she's a duke's daughter and he's a royal...
if this "brother" ends up being MC's father than that means she's a member of the imperial family already.
MAYBE THE BROTHER IS HER FATHER?!!!