On her thirteenth birthday, June 12, 1942, Anne received a red-and-white checkered autograph book that she decided to use as a diary. Just weeks later, the family went into hiding in the Secret Annex—a concealed section of rooms behind Otto's business at 263 Prinsengracht. For twenty-five months, Anne, her family, and four other Jews lived in cramped quarters, completely dependent on a small group of courageous helpers who risked their lives to provide food, news, and supplies. During this time, Anne transformed her diary into an extraordinary document, writing with remarkable honesty about the fears, frustrations, and hopes of a teenager living in impossible circumstances. She addressed her entries to "Kitty," an imaginary friend, and documented everything from the daily tensions of hidden life to her observations about human nature, her emerging romantic feelings for Peter van Pels (another hidden resident), and her dreams for the future. The Secret Annex was betrayed to the Nazis on August 4, 1944, and all eight occupants were arrested. Anne and her sister Margot were eventually deported to Bergen-Belsen concentration camp, where both died of typhus in February or March 1945, just weeks before British forces liberated the camp. Anne was only fifteen years old. Of the eight people in hiding, only Otto Frank survived. When he returned to Amsterdam, their helper Miep Gies gave him Anne's diary, which she had saved from the raided annex. Otto was deeply moved by his daughter's writing and, recognizing its importance, worked to have it published. "Het Achterhuis" (The Secret Annex) was first published in Dutch in 1947, and eventually became known worldwide as "The Diary of a Young Girl."