You might ask why is a novel, The Hated Son, set in Italy in the 1530s during the wars of The Medici's doing in The Comedie Humaine, which Balzac intended to portray French society circa 1820 to 1840? One answer is Balcaz was having good commercial success with the project so he just threw Tne Hated Son along with a few other historical fictions into editions. Of course there are deeper reasons you can come up with. Italians have a special place in Balzac's world, perhaps more intense than the French.
As The Hated Son begins a count's much younger wife is giving birth after only seven months. The count says if the baby, which he demands be a son, is not born healthy he will kill him and his wife. The son does survive. The father raises him to be a very "manly" lad, no poetry, no flowers, no sentimentality. Compressing a bit, the son becomes a military officer and is killed in battle. The count, whose wife has by now died, remarries and has another son. Now parts of this seem almost silly in literal retelling. The son never reached five foot and has blue eyes so naturally he seems disappointingly in masculine to his father who fears he will never provide him a grandson. The father hates his second son. Of course arranging marriages for children is a very big theme of all literature of the time. The son falls in love with a woman of great delicacy. The count has another woman in mind but his people tell him do not even hint at any thing like sex as it will frighten his son from the idea of marriage. The story line does equate totally how you look with what you are. A short man is not masculine, a blue eyed one overly sensitive, a woman with large breasts cannot be trusted to be faithful. The ending is terrible harsh and violent.
I am enjoyed reading The Hated Son. It is a strange story. The plot is melodramatic but still fun.