The Diary of a Young Girl is a book based on the excerpts from a diary written by Anne Frank while she was in hiding for two years with her family during the Nazi occupation of the Netherlands. The family was apprehended in 1944 and Anne Frank ultimately died of typhus in the Bergen-Belsen concentration camp. After the war, the diary was retrieved by Anne's father, Otto Frank.
In the original notebook her diary entries follow a standard for the first three months until 28 September 1942 when she began addressing her entries to characters from Cissy van Marxveldt's Joop ter Heul novels. In van Marxveldt's books the headstrong Joop also keeps a diary and writes to her group of friends about her calamities and loves. Anne adopted the group and addressed her diary entries to Joop's friends "Kitty", "Conny", "Emmy", "Pop", and "Marianne" until November of that year, when the first notebook ends. By the time she started the second existing volume, there was only one imaginary friend she was writing to: Kitty, and in her later re-writes, Anne changed the address of all the diary entries to "Kitty".
There has been much conjecture about the identity or inspiration of Kitty, who in Anne's revised manuscript is the sole recipient of her letters. In 1986 the critic Sietse van der Hoek wrote that the name referred to Kitty Egyedi, a prewar friend of Frank's. Van der Hoek may have been informed by the 1970 publication A Tribute to Anne Frank, prepared by the Anne Frank Foundation, which assumed a factual basis for the character in its preface by the then chairman of the Foundation, Henri van Praag, and accentuated this with the inclusion of a group photograph that singles out Anne, Sanne Ledermann, Hanneli Goslar, and Kitty Egyedi. Anne does not mention Kitty Egyedi in any of her writings (in fact, the only other girl mentioned in her diary from the often reproduced photo, other than Goslar and Ledermann, is Mary Bos, whose drawings Anne dreamed about in 1944) and the only comparable example of Anne writing unposted letters to a real friend are two farewell letters to Jacqueline van Maarsen from September 1942.
Theodor Holman wrote in reply to Sietse van der Hoek that the diary entry for 28 September 1942 proved conclusively the character's fictional origin. Jacqueline van Maarsen agreed but Otto Frank assumed his daughter had her real acquaintance in mind when she wrote to someone of the same name. However, Kitty Egyedi said in an interview that she was flattered by the assumption but doubted the diary was addressed to her:
"Kitty became so idealized and started to lead her own life in the diary that it ceases to matter who is meant by 'Kitty'. The name ... is not meant to be me."
Anne had expressed the desire in the re-written introduction of her diary for one person that she could call her truest friend, that is, a person to whom she could confide her deepest thoughts and feelings. She observed that she had many "friends", and equally many admirers, but (by her own definition) no true, dear friend with whom she could share her innermost thoughts. She originally thought her girlfriend Jacque van Maarsen would be this person, but that was only partially successful. In an early diary passage, she remarks that she is not in love with Helmut "Hello" Silberberg, her suitor at that time, but considered that he might become a true friend. In hiding, she invested much time and effort into her budding romance with Peter van Pels, thinking he might evolve into that one, true friend, but that was eventually a disappointment to her in some ways, also, though she still cared for him very much. Ultimately, the closest friend Anne had during her tragically short life was her diary, "Kitty", for it was only to "Kitty" that she entrusted her innermost thoughts.