On 25 June 1947, Anne Frank's diary was first published, going on to become a much-loved bestseller worldwide. In this exclusive archive clip, her father, Otto, tells the BBC about his decision to make her words public.

Otto Frank initially couldn't bear to read, let alone publish, his daughter's diary, which was released 57 years ago this week. In 1976, he travelled to the BBC's Blue Peter studio to explain why he did. "I only learnt to know her really through her diary," Otto Frank confessed to Blue Peter's Lesley Judd, as he showed her the personal writings of his beloved late daughter Anne.

Otto had actually given his bright, outgoing daughter an autograph book as a gift for her 13th birthday on 12 June 1942. But Anne had almost immediately decided to use it as a diary and began to record her innermost thoughts, writing as if she was revealing secrets to a close friend. "I hope I shall be able to confide in you completely, as I have never been able to do to anyone before," Otto read out from Anne's first diary entry on the children's TV programme. "And I hope you will be a great support and comfort to me."

Otto had fled with his family to Amsterdam in 1933 from Frankfurt, where Anne had been born, following the Nazi Party's success in the German federal elections and Adolf Hitler being appointed Chancellor of the Reich. But the safety the Dutch capital seemed to offer from the looming threat of the Nazis would prove to be only a temporary reprieve for the family. In 1940, Hitler having now seized power and declared himself Führer, invaded the Netherlands. With German occupation came a wave of antisemitic measures. Jews were prohibited from owning businesses, forced to wear identifying yellow stars and faced curfews.

Otto, like many Jews, had been attempting from 1938 to emigrate to the US, but the lack of an asylum policy, and the lengthy process to acquire a visa, meant that the paperwork couldn't be completed before the Nazis shut US consular offices in all German-occupied territories in July 1941.

A month after Anne's birthday in 1942, Otto's older daughter Margot received a call-up notice to report to a German labour camp. To evade the authorities, the whole family moved into a secret annex Otto had discovered above his business premises in Amsterdam. For the next two years, the Frank family hid in that space, along with another family and a family friend. In the stifling confines of the annexe, everyone living there was forced to remain silent during the day, and were unable to use the toilet until night-time when the office cleared, for fear of being heard. Food and supplies were smuggled in by a small group of trusted helpers.

All this time, Anne kept scribbling her thoughts in her diary in........

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