Ekaterina Goncharova's story is interesting. According to her French Wikipedia article (Google translation), "She spent her childhood and teenage years in Moscow, where he received a good education.
In the fall of 1834 at the invitation of his younger sister, Natalia, wife of Alexander Pushkin, Ekaterina moved to St. Petersburg with her in the house of Pushkin. In December of the same year she became a maid of honor to the Empress. (The Empress is Alexandra Feodorovna - gogm)
Ekaterina met Georges-Charles d'Anthes in the fall of 1834, shortly after moving to St. Petersburg. Their wedding took place January 10, 1837, in two ceremonies: one Catholic and one Orthodox. The couple had four children.
She died Oct. 15, 1843, due to puerperal fever after giving birth to her son."
According to his Wikipedia article, George Charles d'Anthes was an Alsatian aristocrat and military officer who supported the Bourbons and not the Orléanists in 1830 so he went back to Alsace and then was allowed to serve abroad. He ended up in St. Petersburg. There he joined the Knights Guards and also met and married Ekaterina.
He also met the Dutch plenipotentiary to the court, Baron Heeckeren. Baron van Heeckeren was childless and did not want his title to become extinct. "After a lengthy correspondence and a journey to Alsace, the latter (Baron Heeckeren - gogm) proposed to d'Anthès's father to adopt the son as his heir. After the agreement of the King of the Netherlands, Georges-Charles d'Anthès took the name of Georges-Charles de Heeckeren d'Anthès."
"D'Anthès met Pushkin and his wife, Natalia ("Natasha"), a beautiful and flirtatious young woman who had many admirers. D'Anthès courted her in such a way that Pushkin threatened him. D'Anthès then married Natalia's own sister, Yekaterina Goncharova, on 10 January 1837. It has been suggested that d'Anthès's engagement and marriage to Natalia's sister was devised to contradict society gossip that he was in pursuit of Natalia. In any event, this was not enough to soothe the conflict between the two new brothers-in-law, especially since an anonymous letter nominated Pushkin Deputy Grand Master and Historiograph of the Order of Cuckolds. Pushkin's jealousy made him write an insulting letter to d'Anthès's adoptive father. Pushkin having refused to withdraw these abuses, a duel became inevitable." Baron d'Anthes fired first, fatally wounding Pushkin.
I don't know if there is a romance novel that can match this.