And then Gilles takes Sophie (a girl he doesn't, indeed can't, love) to Hungary, where Fabien is on location for a new movie and staying with Annabel until she falls out with him again and Gilles takes Annabel back to Paris, leaving Sophie to spend the rest of the holiday in Hungary.
And for three weeks Gilles's dreams come true and Annabel welcomes him into her bed and he lives with her in her flat. But Fabien returns, Gilles thinks Annabel will go back to him, gathers his belongings and leaves the key in the letter box. To Annabel's anger.
When Fabien buys a place in Neuilly and Annabel moves in with him she finds she's pregnant. She's told Fabien that she had a relationship with a man far older than Gilles (just to put her fiancé off the scent) while they split up, and when the child is born Gilles advises his brother to have a DNA test: it proves negative, and Fabien throws Annabel out.
Meanwhile Gilles has gone back to Sophie (although of course he's never stopped loving Annabel), who gives birth at the same time as Annabel, and Gilles knows, but doesn't care, that the baby is really Fabien's, and he's still marrying Sophie.
And then there's a potential atom bomb when Gilles tells Fabien that Annabel's baby is really his, although he knows that she'll deny it. Gilles's mother Catherine disowns him, but then her affections are for Fabien anyway, and shortly after Catherine tells her younger son that his father is in fact not the man who brought him up, he dies in a motorcycle accident.
So Fabien is only Gilles's half-brother, his wife's baby is not his but his half-brother's, he's the father of Annabel's child, and as Annabel and Fabien never marry, the 'Sister-in-Law' of the title must refer to Fabien's posthumous relation to Sophie!
Gilles says that Sophie and Catherine know that Annabel's lied about the true father, but they just continue to make believe that he's the liar. Well, has the reader ever suspected Gilles as an unreliable narrator? What does Gilles care: he only loves Annabel, who's bringing up their son, and every day he gets to take care of his reborn (half-)brother.
(In an article published in the magazine Le Point on 1 December 2011 and entitled 'Eva Joly, présidente de la République', Patrick Besson mocked the French-Norwegian green presidential candidate's accent by writing the whole piece in a kind of mock-Germanic style which began: 'Zalut la Vranze ! Auchourt'hui est un krand chour : fous m'afez élue brézidente te la République vranzaise'. It was the subject of some debate, and Joly called the article a 'racist attack', whereas Le Point didn't see what the fuss was about, and spoke of 'the dictatorship of the politically correct'. Some internautes tried to defend Besson by turning to the world of fiction and pointing out that Balzac too made fun of accents, as in the Alsatian Schmucke in Le Cousin Pons. Besson's article (with comments)).
My other Patrick Besson post:
Patrick Besson: Assessible à certaine melancolie