January 31 1939 sounds like an auspicious date for a dreamy teenager to begin her diary. And so it was for Renia Spiegel, a Polish Jewish girl living with her sister and grandparents in Przemysl. “I just want a friend”, she says in her opening entry, when she was 14, “somebody who will feel what I feel, believe what I say and never reveal my secrets”.

Over the next 700 pages, full of adolescent yearnings and fantasies, there are 60 poems and intricate discussions of Renia’s life, her friends, her crushes on boys, her longing for her mother, her desire to travel to France.

What there is very little of, considering the time and place, is the increasing narrowness of Renia’s world. Her capacity for looking on the bright side of life and her joyous adoration of her boyfriend, Zygmunt Schwarzer, with all the ups and downs of a teen romance, are faithfully recorded.

But there are scant references to the encroaching Nazi grip on the Jews of Przemysl. Only by close reading of the diary can we learn about Renia’s move into the ghetto, of how she, like other Jews, was made to wear a white armband, of her anxiety in obtaining the correct work papers.

Renia turns 18 in June 1942, and then the diary abruptly ends on July 25. An obviously terrified Renia writes: “My dear Diary, my good, beloved friend! We have been through such terrible times together and now the worst moment is upon us”.

She ends her diary entry committing herself to God. But the next entries are not from Renia, but from Zygmunt. On July 31, 1942, he records: “Three shots! Three lives lost! It happened last night at 10.30 pm. Fate decided to take my dearest ones away from me. My life is over. All I can hear are shots, shots… shots. My dearest Renusia, the last chapter of your diary is complete”.

And that might have been the last the world heard of Renia Spiegel, but for two dramatic twists. She may not have survived, but her diary did — and so, miraculously, did Zygmunt Schwarzer. It was his parents who were murdered along with Renia after they were found hiding together by local Nazis.

And two other survivors are vital to this story — Renia’s mother, and her little sister, Ariana Spiegel.

Ariana Spiegel is today known as Elizabeth Bellak, a tiny, bird-like woman of 89, who lives in New York and who becomes more and more animated as she talks about her sister and her diary. It’s not hard to imagine Ariana as she once was known throughout her homeland — the Polish Shirley Temple. For if Renia, six years older than Ariana, was known for writing and love of languages then Ariana was known for singing and dancing. She was a child star in several films.

She did not know that her sister was even writing a diary, so private did Renia keep it. And she is called Elizabeth Bellak, née Lesczynska — because her life and that of her mother Roza were saved after they converted to Catholicism — and they stayed converted, even when they arrived in New York in December 1946.

“For some weird reason”, Elizabeth says today, “Zygmunt, my sister’s boyfriend, tracked my mother down in the 1950s”. It was extraordinary that he managed to find the former child star and her mother, with their radical name and religion changes.

By then Zygmunt had gone to medical school and qualified as a doctor. “The Germans [after 1945] paid for Jews to go to school,” says Elizabeth, “and he had been through the camps but then went to school in Heidelberg. And he found us, and he gave my mum Renia’s diary. We never asked him what had happened to the diary during the war”. She thinks Zygmunt had given the closely-written pages to a Polish friend for safe-keeping, and an unknown friend had returned the diary to him when he had emigrated to America.

Zygmunt had done his best to hide his own parents together with Renia. “His mother’s brother was some sort of big shot in the Judenrat [the Jewish Council] and he lived outside the ghetto. And he found them this hiding place”. But the secret was discovered, and all three were killed; the uncle himself ended up in Auschwitz, says Elizabeth.

Zygmunt was “an adorable guy, very handsome, always smiling,” says Elizabeth. “He used to come to the house, and sit in the corner with my sister. I knew him well. He had green eyes, black curly hair, very personable”.

And it was Zygmunt who, after the deaths of Renia and his own parents, risked his life to rescue the 12-year-old Ariana and take her out of the ghetto. He took her to the non-Jewish Polish family of her best friend, whose father Ludomir Lesczynska, with great courage, reunited her with her mother. With false papers and Catholic baptism certificates, they survived the war and eventually made it to America.

Neither Elizabeth nor her mother had had any idea about Renia’s diary — but neither of them could bear to read it. And, though Elizabeth saw Zygmunt a few times in New York, it was not so comfortable. He had married a woman, also a survivor, called Genia, and had virtually turned his basement into a shrine to Renia.

“He had made copies of every page of the diary, and used to pore over the pages, and had pictures of her on the wall. Genia wasn’t so friendly to me”.

Elizabeth’s mother, who died in 1969, kept the diary hidden in her personal possessions. After her death, Elizabeth locked it away in a Manhattan bank vault. Elizabeth and her husband George Bellak, a Jewish emigrant from Vienna, had two children, Michael and Alexandra, but she only told them about their Jewish heritage when they were about 12. And this sparked the curiosity of Alexandra, who has accompanied her mother to London.

“It became her mission”, Elizabeth says of Alexandra. The mission was not so much to find out about being Jewish, but to find out about the diary and its contents.

At Alexandra’s instigation, the diary was taken out of the bank and serious consideration given to getting it translated into English. A film-maker, Tomas Magierski, helped with researching Renia’s and Elizabeth’s early lives, unearthing photographs, documents, and even film clips of the Polish Shirley Temple singing and dancing. Curiously, however, there are no records — either in Poland or Yad Vashem — of Renia’s death, or of Zygmunt’s parents, or even Renia and Elizabeth’s grandparents, with whom the sisters were living in Przemysl. So no one knows where Renia was buried. And nor has it been possible to find out what became of the girls’ father, who was separated from their mother and may have ended his life, together with their cousin, in another ghetto near their town.

What did Elizabeth think Renia would make of today’s level of recognition? “I was thinking this myself, reading some of the diary and crying a little. But I think she would probably have thought it was OK: she was the head of the literary circle at school. Whenever the school needed something to be written, she would win the first prize for a poem. She was tremendous. She was very talented. I was very different from my sister; I’m very outgoing and lively. My sister was quiet, reserved… always thinking about things. But she was very grown-up, she took care of me and was my surrogate mum”.

“In the end,” says Elizabeth, “I know that my words are the legacy of the life my sister didn’t get to have, while Renia’s are the memories of a youth trapped for ever in war”.

‘Renia’s Diary’ is published this week by Ebury