Background: Vladimir Vladimirovich Nabokov (; Russian: Vladimir Vladimirovich Nabokov, pronounced [vla'djimjIr na'bok@f] ( listen), also known by the pen name Vladimir Sirin; 22 April [O.S. 10 April] 1899 - 2 July 1977) was a Russian-American novelist, translator and entomologist.
Context: In March 1922, Nabokov's father was fatally shot in Berlin by the Russian monarchist Piotr Shabelsky-Bork as he was trying to shield the real target, Pavel Milyukov, a leader of the Constitutional Democratic Party-in-exile. This mistaken, violent death would echo again and again in Nabokov's fiction, where characters would meet their deaths under accidental terms. (In Pale Fire, for example, one interpretation of the novel has an assassin mistakenly kill the poet John Shade, when his actual target is a fugitive European monarch.) Shortly after his father's death, Nabokov's mother and sister moved to Prague.  Nabokov stayed in Berlin, where he had become a recognised poet and writer within the emigre community and published under the nom de plume V. Sirin (a reference to the fabulous bird of Russian folklore). To supplement his scant writing income, he taught languages and gave tennis and boxing lessons. Of his fifteen Berlin years, Dieter E. Zimmer has written: "He never became fond of Berlin, and at the end intensely disliked it. He lived within the lively Russian community of Berlin that was more or less self-sufficient, staying on after it had disintegrated because he had nowhere else to go to. He knew little German. He knew few Germans except for landladies, shopkeepers, the petty immigration officials at the police headquarters."  In 1922, Nabokov became engaged to Svetlana Siewert; she broke off the engagement in early 1923, her parents worrying that he could not provide for her. In May 1923, he met a Russian-Jewish woman, Vera Evseyevna Slonim, at a charity ball in Berlin and married her in April 1925. Their only child, Dmitri, was born in 1934.  In 1936, Vera lost her job because of the increasingly anti-Semitic environment; also in that year the assassin of Nabokov's father was appointed second-in-command of the Russian emigre group. In the same year, Nabokov began seeking a job in the English-speaking world. In 1937, he left Germany for France, where he had a short affair with Russian emigree Irina Guadanini. Yet the family followed him to France, making enroute their last visit to Prague, then spent time in Cannes, Menton, Cap d'Antibes, and Frejus and finally settled together in Paris. In May 1940, the Nabokov family fled from the advancing German troops to the United States on board the SS Champlain, with the exception of Nabokov's brother Sergei, who died at the Neuengamme concentration camp on 9 January 1945.
Question: What happen to his mom

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