Fan theories were the life's blood that helped turn Game of Thrones from HBO's odd gamble on dragons into the world's biggest series. The lack of completed novels in the A Song of Fire and Ice drove them. But it was the genre-busting twists that drove fans wild in trying to predict what came next. Though most suspected Daenerys and Jon Snow would fall in love, other theories said Jon would fall for someone else. But Kit Harington's reaction to that Jon & Sansa Game of Thrones theory speaks volumes of how much the cast knew about these guesses, and how offbase some were.
Known as the "JonSa" theory, this alternate ending where Jon and Sansa fall in love has its roots in the original outline Martin wrote back when he envisioned the series as a trilogy. It's a far less complicated story, where there are only five main POV characters: Tyrion, Daenerys, Bran, Arya, and Jon Snow. Sansa exists as a character, but her fate in this version is more tragic, wedding and bedding Joffrey, and bearing him a son, causing her to choose the Lannisters side in the war.
So how does that lead to a Jon and Sansa relationship? In this version, Jon does not fall in love with Dany – instead, he winds up falling in love with a much more feminine Arya. They are the "incestuous love story" instead of the Lannisters. (Cersei doesn't even exist in this version, only Jaime, who in this version is the one who kills everyone to ascend the Iron Throne.) According to Martin's outline:
Their passion will continue to torment Jon and Arya throughout the trilogy until the secret of Jon's true parentage is finally revealed in the last book.
Some fans were, therefore, perhaps somewhat understandably, convinced this outline was still partly correct. Not with Jon falling for Arya, of course, her story changed radically. Instead, it would fall to Sansa, whose story now followed Arya's original arc back to Winterfell. When Jon Snow and Sansa joined forces in Season 6, the "JonSa" theory gained traction that an unexpected twist would lead to Jon and Sansa as the show's final love story.
But according to The Sun, when asked about it, Harington, who played Jon, was thunderstruck at the idea. Moreover, the idea was so foreign to him, that he reacted with genuine disgust.
They wanted Jon with Sansa?! What? No! What? That's weird!
To be fair, it's no weirder than Cersei and Jaime. And falling in love with Sansa (and listening to her about Daenerys) might have saved a few thousand lives in King's Landing to boot. But that's not how things turned out. Instead, Jon and Sansa got far better happy endings than marriage, winding up in their loved ones most.