Note: Spoilers ahead.
Fans of both Game of Thrones the TV show and Game of Thrones the book series likely noticed a disturbing plot discrepancy between the two while watching Sunday night's episode "Breaker of Chains," when Jaime Lannister raped his sister Cersei beside the body of their dead son. While plot changes aren't unheard of for the HBO show, what made this particular scene so controversial is that in George R. R. Martin's book, the sex is portrayed as consensual (albeit still incestuous and horribly morbid).
While the episode's director Alex Graves told Vulture that the scene "was meant to be consensual," viewers couldn't justifiably argue that it was portrayed that way. Cersei says "no," "don't" and struggles throughout the entire scene. If consent was given, it didn't make the final cut.
After the episode set off both fans and critics, Martin himself has weighed in on the scene in the comments of his blog to speculate why the show chose to make such a change:
I think the "butterfly effect" that I have spoken of so often was at work here. In the novels, Jaime is not present at Joffrey's death, and indeed, Cersei has been fearful that he is dead himself, that she has lost both the son and the father/ lover/ brother. And then suddenly Jaime is there before her. Maimed and changed, but Jaime nonetheless. Though the time and place is wildly inappropriate and Cersei is fearful of discovery, she is as hungry for him as he is for her.
The whole dynamic is different in the show, where Jaime has been back for weeks at the least, maybe longer, and he and Cersei have been in each other's company on numerous occasions, often quarreling. The setting is the same, but neither character is in the same place as in the books, which may be why Dan & David played the [scene] out differently. But that's just my surmise; we never discussed this scene, to the best of my recollection.
Martin has discussed his theory of "the butterfly effect" before, which centers on the idea that any deviation the show makes from his intricate plot will logically lead to further deviations later on. Regarding Jaime and Cersei's scene, Martin keenly noted another crucial difference between the books and the TV series, namely that the books tell the story from different characters' points of view. Due to the nature of television, scenes can't quite be cast in that way:
I was writing the scene from Jaime's POV, so the reader is inside his head, hearing his thoughts. On the TV show, the camera is necessarily external. You don't know what anyone is thinking or feeling, just what they are saying and doing.
If the show had retained some of Cersei's dialogue from the books, it might have left a somewhat different impression -- but that dialogue was very much shaped by the circumstances of the books, delivered by a woman who is seeing her lover again for the first time after a long while apart during which she feared he was dead. I am not sure it would have worked with the new timeline.
That's really all I can say on this issue. The scene was always intended to be disturbing... but I do regret if it has disturbed people for the wrong reasons.