Who is cecil?
Cecil refers to the ML of this manga/novel: http://www.mangago.zone/read-manga/jishou_akuyaku_reijou_na_konyakusha_no_kansatsu_kiroku/
Spoiler:
Cecil who finds that his son has a deep obsession with his mother (Cecil's wife) ends up learning and encouraging his son to turn his obsession from the mother to the sister, hence turning his son from a momma's boy to a sis-con. This way, Cecil, who is also obsessed with his wife, can have her to himself.
By the way, the novel is completed while the manga is almost finished. The novel is pretty short and readable!
Beat me to it but yeah. Prince Cecil be original Machiavellian mind behind this nefarious scheme.
How to get your psychotic mother-con son to lay off his obsession... Turn him into a sis-con instead. I can see Cassius went the Cecil route.