Hux sr is in a long term established (read abusive & controlling) relationship with his son. Hux jr wouldn't even think of disobeying his father, not even when his father tells him he wants him to carry his child to keep the bloodline clean.

Lots of impregnation kink from Hux sr who really gets off on this

Bonus if Kylo finds out and is disgusted with Hux sr (but also has feelings for Hux jr)

if you want to make a really dark turn (entirely optional) the impregnation was a 'reward' for finishing the Starkiller Base and in the aftermath HUx sr forces his son to have an abortion because he's not 'worthy' anymore after his failure

(I blame all of this on the kylux & hux sr/hux I just read)