Sibling incest is a tale as old as time—and it’s not going away

For two seasons, siblings Cesare and Lucrezia Borgia participated in Vatican scheming, suffered heartbreaks and betrayals, and trusted only one another; there’s so much romantic tension between them that characters can’t seem to stop commenting on it. (There are even mythical references, as during a Old Rome banquet at which Lucrezia dresses as Echo, the lonely woman doomed to fall in impossible love.) For two seasons the Borgias producers were clear that they weren’t going to cross the line into incest, and as Lucrezia suffered a humiliating marriage and Cesare chafed at the clerical collar, their mutually grim storylines were alleviated only by one another. It was enough bedrock that when the producers got word they’d be renewed for a third season but not a fourth, they threw caution to the wind and let Cesare and Lucrezia consummate the unspoken. And their established sexual relationship managed to complicate rather than diminish the siblings; they’d been close for so long, and so miserable apart, that the sex felt more like a relief than a taboo.

Their pairing was both passionate and relatively sanctioned by the show (Lucrezia speaks of God in the room with them as sincerely as any myth), and became the only emotionally weighty romance the show ever managed. They even had a love theme that began to overlap scenes of the show’s many political machinations, a reminder that this relationship was powerful enough to change the course of Rome—and their arc ended in a moment of such Byronic intimacy (as Cesare wipes her husband’s blood from her face) that it suggests the engine of their romance had pushed them past even their elevated status and made them somehow superhuman in their love for one another. It’s not a far reach; they had the advantage of being built up separately long before the relationship became text (so audiences got to anticipate the inevitable with more preparation than, say, Justin and Iris), but it also seemed as though, amid the Vatican scheming, incest between two loving siblings was as pure a love as anyone was likely to find.

Of course, that’s the trick about incestuous siblings, no matter where they fall. While incest can always be used as a neat shortcut to signal darkness or conflict, the mythic element of it actually rests on the subtext of the inexorable fate of those thwarted souls, which is almost always framed as outside the control of the siblings in question. On television, incest defines and directs the people in it in a way that occurs in very few other relationships; the happiness or sadness of a relationship of sibling incest is preordained by the narrative, and the characters powerless to fight against it. (They have to be, for this to work; no one chooses to break the taboo unless circumstances are somehow beyond their control.)

This is the essential storytelling trick that conjures enough sympathy to temper the inherent voyeurism of waiting for imaginary blood relatives to cross the line and kiss. And as the audience is asked to accept that the power of their feelings is strong enough to smash a taboo, we accept the underlying understanding that such closeness is only possible under awfully specific terms; a wrong thing, maybe, but also a rare one, and one that wields a power on the story greater than the sum of its parts. Cesare’s a sucker for Lucrezia and is willing to tear Italy apart to reunite with her; Justin and Iris are each other’s only true believers in a quest that comes with a body count, and Cersei and Jaime started a war trying to keep one another close.