Who was Georges D’Anthès, and how is he related to a poet's death?

Georges D’Anthès was the man who killed the famous Russian poet Alexander Pushkin in a duel. The adopted son of the Dutch Ambassador, D’Anthès was a dashing young French cavalry officer who entered the Russian Army to advance his military career. It was while serving with the elite Knights Guard regiment that he first met Pushkin and his wife, Natalya.
Rumors soon spread that D’Anthès was having an affair with Pushkin's wife; although, it's never been established for certain if those rumors were true. In any case, Pushkin received an anonymous letter informing him that he'd been elected a member of "The Most Serene Order of Cuckolds." A cuckold is an old-fashioned word for a man whose wife is cheating on him.
It's never been established who actually wrote the letter, but Pushkin was certain it was the handiwork of D’Anthès. As was customary at the time, he challenged D’Anthès to a duel as a means of restoring his impugned honor. During that duel, Pushkin, though a veteran of several such encounters, was mortally wounded in the stomach. For his part, D’Anthès was stripped of his rank and banished from Russia for good. He headed for France, where he subsequently carved out a relatively successful career in politics.