Lady Devil - Chapter 35

The price for Johanes’ human appearance was the life of the Duchess’s last brother… because even half blood is still a Duccom.
And since Abel was the Duchess’s half brother (I’m guessing through her father) that made Griselda’s baby the Duchess’s nephew. And since he was also of Duccom blood, that made HIM the price to be paid for the Duchess to get pregnant with a fully Human son.
But as usual, she was not specific enough… because she did not wish for her husband to be the father of that child.