"Swapped at Birth" has a ridiculous script by untalented Fistopher Nolan. Not believable for a second, it has parents Brandi Love and Eric Masterson having plotted for18 years to hump their newborn girl, but making it legal by not only waiting that length of time to reach the age of consent, but also by arranging to trade their kid for another girl at the hospital so it won't be incest. Quite a stretch in order to qualify as a variation on the step form of faux incest.
They break the news to their daughter Jane Wilde on her birthday, and after she gets over the shock of her parents not really being her parents immediately they have a threesome.
I hate the notion that porn is so intrinsically moronic that anything goes. The real surprise here is that the players go along with the gag and pretend this scene makes any sense at all.