The Undying Past is an 1894 novel by the German writer Hermann Sudermann. Its German title is Es war which means "it was". The novel tells the story of how a German man, Leo, returns to his homeland after several year in South America, only to find that Ulrich, his beloved childhood friend, has married a woman with whom Leo has a dark past. The book was published in English in 1906, translated by Beatrice Marshall.
William Lyon Phelps wrote about The Undying Past in his 1918 book Essays on Modern Novelists:
The most beautiful and impressive thing in Es War is the friendship between the two men—so different in temperament and so passionately devoted to each other. A large group of characters is splendidly kept in hand, and each is individual and clearly drawn. One can never forget the gluttonous, wine-bibbling Parson, who comes eating and drinking, but who is a terror to publicans and sinners.
Metro-Goldwyn-Mayer adapted the novel into the 1926 film Flesh and the Devil. The film was directed by Clarence Brown and starred Greta Garbo, John Gilbert, Lars Hanson and Barbara Kent.