I'm currently roleplaying as my brother in CKII - used ruled designer to put him in the fractured Italy around a 1330 start date - and managed to form the Kingdom of Italy within two decades. Anyways,
to prove to y'all that my CKII games aren't just about monogamous sibling incest, here's a nice little fluff story from that game:
So at the start of the game, I was hunting for highly skilled people to invite my court to be my councillors when I came across an English girl of 17 years who was apparently a very nice sweet person based one her traits (kind, chaste, zealous, attractive, etc. traits). Apparently, though, she had a newborn daughter but had no lover or spouse - ie the daughter was a bastard who had no official father. After digging a bit I discovered that apparently an English Earl seduced her for a one night stand and then abandoned her for his five other lovers. I'm not sure why, but I just felt so bad for the girl, because she actually had really good stats and traits and got knocked up by that douche (the guy actually had a bunch of bad traits, just to make it more cliched).
So, thanks to the feels I was feeling, I invited her to my court and married her to a nice young man in my court who had similar traits, and made her my steward since her stewardship was ridiculously high for someone withou a genius/quick trait. I liked to think of it as me giving her another chance in life. We became friends, anyways, and her daughter somehow also ended up friends with my eldest son so I just married those two since they're kinda like brother and sister they seemed a good match traits-wise and her daughter has some good stats. Anyways, so that naive teenage girl that once got seduced and knocked up by a douchey earl basically managed the economy of the Italian principality that would unite Italy, had a successful marriage with a skilled Italian General who would later become a Doge, and whose daughter - once a bastard rejected by the earl - will one day be queen of Italy. I'm guessing she's also probably making tons of dough on the side as a result of her activities and sending that earl random extravagant gifts just to taunt him and insert some other cliched movie scenes
That said, though, I think I'm marrying my second son to my third daughter, since they're my only children who didn't get any good congenital traits.
EDIT: Knowing this is CKII, though, what's probably gonna happen is the daughter is going to die in childbirth, then my eldest son gets depressed and dies from depression, then I myself am going to die early for some stupd reason, then my second underaged son becomes king with the doge as regent, but due to court intrigue the doge and she herself will get killed in some stupid plot, Italy will fall into civil war, and then I get a game over as the HRE/Egypt/ERE/Mongols/Timurids conquer us.