This was the subject of Valérie Donzelli's film Marguerite et Julien (2015), adpated from the novel Julien et Marguerite by Jean Gruault and first offered to but rejected by François Truffaut in the 1960s. The brother Julien de Ravalet (Jérémie Elkaïm) and sister Marguerite de Ravalet (Anäis Demoustier) were the beloved children of Jean de Ravalet (Frédéric Pierrot), the lord of Tourlaville and Madame de Ravalet (Aurélia Petit) had been inseparable since infancy: playing, drawing, studying, riding, sleeping together and as children they swore to each other that they will always love each other and will never abandon the other. But when they reach puberty, Julien was sent with his elder brother Philippe (Bastien Boulllon) to England, Holland and Germany to receive training in finance, commerce and weapons. When they returned, it was time for Marguerite to get married. On the day of the arranged marriage, first Julien excused himself from the dinner table in the middle of the wedding reception, then Marguerite did the same shortly thereafter. After an unduly long time, the family of the bridegroom stormed out. The brother and sister were subsequently found at the stables by Madame de Ravalet, in the middle of an intimate game of guessing the word written first on the palm and then on each other's back. The word got around and no further suitors could be found and finally Marguerite's parents married him to the only available choice, the very wealthy local tax inspector Lefebvre (Raoul Fernandez), at the family chapel by their paternal uncle, the Abbé de Hambye (Sami Frey), Julien absenting himself from the ceremony.
The story, as told as a bedtime story or even a sort of "legend" to the little girls of an orphanage, did not end there. After the marriage, Marguerite refused to consummate the matrimonial union in bed, forcing Lefebvre to relieve himself at brothels and drinks. Marguerite found her life with the Lefebvres an unendurable torture and suffocating. Her only consolation was the exchange of love letters with her brother through their family servant acting as clandestine intermediary. But the exchange of billet doux came to an abrupt end when Lefebvre's spies found out and Lefebvre put a bullet through her chest. The situation had become urgent. Julien planned a nocturnal escapade communicated to Marguerite through a boy chimney-sweep. It was successful, but not for long. They were pursued to the coast by the police upon a tip off from Lefebvre's spies. Julien had made arrangements for a sea voyage to England, where they'd change their names and live as husband and wife and give birth to their child. But at the last minute, the police arrived. They were caught and brought to trial and convicted of incest and assaults etc.When the film ends, we see Jean and Philippe carting away the infant child of Marguerite and Julien, also given the name Julien, away on the coastal prison where a while ago, they had their heads chopped off with an axe.
To lend an air of myth or fairy tale to the story of this forbidden love, Donzelli resorted to a variety of stylistic devices: interspersing as background music in different scenes contemporary English ballads, Medieval music, 19th century romantic music, images of characters suddenly moving again from frozen frames, horse carriage moving alongside early 20th century motor cars, images of Marguerite being taken away separately from her brother by a helicopter during their arrest, images of the pre-teen brother and sister running around on a beach with a helicopter hovering in the sky in the background, the recitation of a poem amidst colorful images suggesting freedom in another world, a calculated hodge-podge of postmodernist tricks for the deliberate fuzzying of the boundaries of space and time. The result is to produce an air of unreality and distance to what is being recounted. I do not know if the true intention behind what Donzelli is trying to do is to engage our intellect, not just our emotions through the use of a contemporary adaptation of the so-called "alienation effects" first made famous by the German dramatist and Marxist theoretician of the theatre Bertolt Brecht, so that instead of being merely emotionally engaged by what is going on on the screen, we will be forced to reflect rationally about the moral, social and political implications of the meaning of "sibling incest" as a category in general through the particular example of a late 16th/early 17th century brother and sister couple who suffered such a horrible termination of their lives when all they were trying to do is to love one another with all their heart and all their soul, in complete disregard of the niceties of social mores and legal sanctions and to show if possible that it's not just a simple matter of right and wrong, good and evil and of being socially and religiously forbidden or prohibited. If she is, she has certainly succeeded with me. I understand that the German Ethics Council has recommended in September 2014 that the government abolish the law criminalizing incest between adult siblings on the ground that such bans impinge on civil right and that Sweden already permits marriage between half-siblings provided they receive counseling. But I am sure that whether incest within the relevant degrees of consanguinity should be permitted by various jurisdictions will remain controversial for a long time to come. For those interested, there is an interesting article on the subject of "incest" in general in the Wikipedia. As a filmgoer, however, I found it sufficiently interesting so that my interest did not flag at any point during the viewing. One may not agree with all the tricks that Donzelli is pulling on our conventional artistic sensibilities, but one can hardly ignore the issues on which that she is trying to engage our attention.