On Friday 7 January 1944, Anne Frank confessed her love for a boy she had been smitten with for years. She had first set eyes upon him in school in 1940, and they had been 'inseparable' for a whole summer, walking hand in hand through their neighbourhood in Amsterdam, him in a white cotton suit, her in a short summer dress. He was 'tall, slim and good-looking, with a serious, quiet and intelligent face'. He had dark hair, brown eyes, a slightly pointed nose. Anne was 'crazy about his smile', which gave him a mischievous air. At one point he gave her a pendant as a keepsake. This was the boy she hoped to marry.

His name was Peter Schiff, he was almost three years her senior, and it is clear from her diary that he was seldom out of her thoughts throughout her two years in hiding in the secret annexe behind her father's office. On 6 January 1944 she wrote that her image of him was so vivid that she didn't need a photograph, but anyone who has read her diary may be curious to see what he looked like at the time she knew him.

Until now, no portrait of Peter Schiff has come to light. But the picture you see opposite has ended this 60-year mystery and provided another glimpse into a devastated world. The photo does its trick - it shows an extremely handsome boy of 12 full of hope for the future; it is not difficult to see his appeal to any vivacious and eager girl of similar age - but the background to its recent discovery provides something more, another layer in one of the most iconic stories of our time.

The story of Anne Frank is one of bravery and fortitude. Her journal, the Diary of a Young Girl, continues to be read anew by hundreds of thousands each year not just for the insights it brings us into occupied Europe, or the practical details we glean about hiding in cramped conditions with limited resources. It is also a story of a bright Jewish girl's transition to adulthood, a maturing of intellect and sexuality and all the possibilities and challenges this brings. At times her diary is a catalogue of frustration and insecurity, but it is all-involving, a saga of peril and yearning written with exceptional emotional insight and cadences that, judging by the teenage blogs of today, we may have lost for good. But the romantic longing and crushes she experienced are timeless and universal, and anyone who has ever lost in love will sense their eyes swell with tears as she writes of Peter Schiff. Anne Frank's life and writing is not emblematic of the 6 million who died; it is far more powerful as a single voice. Since its first Dutch publication under the title The Secret Annexe in 1947, total sales have been estimated at more than 35m.

Anne Frank was born on 12 June 1929 in Frankfurt am Main. She moved to Amsterdam with her family following the Nazis' rise to power in 1933, but became trapped by the German occupation of the Netherlands in 1940. She moved from a Montessori school to a Jewish one, and her life became a series of restrictions and limitations. In June 1942 she received a notebook for her 13th birthday, and her commonplace observations were usually accompanied by darker allusions. The preceding months had seen the Frank family dispose of much of their furniture and other possessions as her father planned the flight from their house to a number of rooms at the back of his office by a canal in the western quarter of the city. A move was set for 16 July, but circumstances forced a move 10 days earlier. Decoys were set: the house was made to look like it was vacated in an emergency; a note suggested their destination was Switzerland.

Anne shared her back rooms with seven others: her mother Edith, father Otto and sister Margot, a family friend named Fritz Pfeffer and the van Daan family (real name: van Pels), and much of her writing describes the jostling for position within their confined environment. She disguised the identity of the family who concealed them and brought them food and news of the outside world, and she addressed most of her diary entries to 'Dearest Kitty', a technique that prompted both a confessional style and the prospect of response. Despite her desire to become a published author, she intended her diary to remain private. But as the war progressed she began to realise the potential educational value of her writing, and she edited entries she judged to be too exposing.

At times her head is full of jealousy and self-doubt, but her mood is levelled by her memory of one boy. 'You mustn't think I am in love with Peter [van Daan], because I'm not... This morning I woke up just before seven and immediately remembered what I'd been dreaming about. I was sitting on a chair and across from me was Peter... Peter Schiff... the dream was so vivid... Peter's eyes suddenly met mine and I...#8239;stared for a long time into those velvety brown eyes. Then he said very softly: "If only I'd known I'd have come to you long ago." I turned away abruptly, overcome by emotion. And then I felt a soft, oh-so-cool and gentle cheek against mine, and it felt so good, so good.'

When she woke up she could still feel his cheek against hers, and his eyes 'staring deep into my heart'. She believed he knew how much she had loved him 'and how much I still do'.

She had a nickname for him, Petel. On 7 January 1944, she writes of being kissed by her father, and wishing it was Peter. 'All day long I've been repeating to myself, "Oh Petel, my darling, darling Petel ..."' Later in the entry she asks: 'Where can I find help? I simply have to go on living and praying to God that, if we ever get out of here, Peter's path will cross mine. Once, when Father and I were talking about sex, he said I was too young to understand that kind of desire. But I thought I did understand it, and now I'm sure I do. Nothing is as dear to me now as my darling Petel!'

As the months progress she wonders if Peter van Daan will serve as a suitable replacement for Peter Schiff, and her suspicious attitude towards him softens towards affection. But at the end of the diary we learn that he has disappointed her. Her last mention of Peter Schiff occurs at the end of April 1944, six weeks before her 15th birthday and three months before her house was raided by the German Security Police. She recalls her dream and the brushing of his cheek, and the intensity it aroused: 'I love Peter as I've never loved anyone.'

Before he moved to Amsterdam in 1939, Peter had another friend. Ernst 'Mic' Michaelis went to school with him in Berlin, and they saw each other whenever they could. Michaelis is now 81, and is a director of Pearson Panke, automotive and aerospace machinery suppliers in Mill Hill in north London. His recollections of Peter Schiff are as vivid as if he had written them in a diary. 'I always had a feeling of elation being with him,' he says. 'As a boy I liked making things, and I had simple woodworking tools and later a metal construction kit. We played with that together. I also had a very grand model railway layout, and we probably played with that as well. We were 11 or 12 years old. I was never bored in his company - I had always liked people who were full of odd ideas, and he was.'

Michaelis was born in Berlin in 1926, and he still speaks with a slight German accent. He remembers that Peter owned an expensive pen, perhaps the one in his pocket in the photograph, possibly bought for him by his mother's new partner (it is believed his father had separated from his mother before the war and moved to the United States). Michaelis also remembers the comfort he felt from being with his friend the day after Kristallnacht, the evening in November 1938 when Jewish homes, shops and synagogues were vandalised throughout Germany and thousands of Jews were escorted to the camps. 'I must have known him for at least a year and a half, possibly longer,' Michaelis remembers. 'He was an intelligent boy, and I think this must have been why he liked Anne - she had a lively mind. You get the impression from her mentions of him that it was all to do with appearance, but I'm sure she would have been bored with him if he'd been stupid.'

Michaelis and Schiff last saw each other in the summer of 1939. Michaelis came to England on the Kindertransport, going to school first in Sussex and then attending Bryanston School in Dorset. Schiff, accompanied by his mother, went to Amsterdam. But before the boys parted they exchanged photographs. Michaelis's picture was taken by a friend of his mother at his home, while Schiff's may have been taken at a professional studio. 'We did not know how else to say goodbye to each other - 12-year-old boys do not promise each other to write letters. We were at my home, but to be together as long as possible I walked with him to his home, about 25 minutes' walk.' Schiff wrote a note using his full name: 'In friendly remembrance of your friend Lutz Peter Schiff' and Michaelis pasted both note and photograph (which was standard passport-size) into an album. A few years later the photograph was transferred to a larger book, where it sat undisturbed alongside other photos and correspondence for several decades. When he first read Anne Frank's diary in the Fifties, Michaelis had suspected that the Peter Schiff in the book was the same boy he had once known. He imagined that Schiff had perished in a concentration camp, but he couldn't confirm this either. In the last few years, however, things have come into focus.

In 2000 he received a copy of Aktuell, a publication sent to refugees from Berlin scattered throughout the world. It carried a class photograph from Holdheim School taken in the spring of 1938, and with it a request for information regarding any of the 25 people pictured in it with their thick winter coats and sunny dispositions. Michaelis recognised it as his class: there he was, number 18, leaning to his left so we could get a good look at him. To his right in the same row, at number 10, was Peter Schiff. But Michaelis had more important things on his mind at the time: his wife Ann had recently been diagnosed with breast cancer. He put the magazine to one side, and forgot about it.

In May 2005 his wife was told there was nothing more they could do for her. She said she would like to pay a final visit to Berlin, but this may have been as much for his benefit as for hers: she was born in London in 1939, and was not Jewish. They had visited the city not long after the wall came down, at a time when large parts of it still resembled a building site, and Ann said she wanted to see what had been built. They visited the Jewish Museum, and she bought a copy of Anne Frank's diary. 'At that time, because of her confused mind, she couldn't read novels, but she could still read biographies,' her husband says. She died four months after their visit.

Last summer, shortly before his two children had found him sheltered accommodation, Michaelis picked up Anne Frank's diary again and began to wonder. 'I realised that there were lots of pictures associated with her life, but no picture of Peter Schiff. That seemed very odd, as his [good] looks are at the heart of his story. I thought that people might be interested in my picture.' He contacted the man who had placed the class photo in Aktuell, and began a correspondence with several of his old classmates. Two remembered Peter Schiff well: 'He was a very likeable and friendly boy,' wrote Ursula Meyer (nee Totschek, number six in the photograph), who now lives in Maryland, 'and I think I had a bit of a crush on him.' Helga Burch (nee Walnau, number two), now residing in California, remembered that he was a 'delightful, funny, alert class clown, the spirit of the class. He once made Dr Gottschalk [the rabbi to the right of the picture] so angry that he hit him.'

When Michaelis searched the internet he found conflicting information, but his research did at least confirm Schiff's date of birth, and that he and Anne Frank shared the same friend.

Michaelis called the Anne Frank Trust in London: they said they didn't have a picture of Peter Schiff and knew very little about him. Then he wrote to the Anne Frank House in Amsterdam (the preserved building where she and her family hid - an educational centre that attracted more than 1m visitors last year), and staff confirmed that they didn't have a picture. They encouraged Michaelis to visit, and earlier this year he made the trip with his children and his grandchildren, and his photograph. 'They were very excited,' he says, and he agreed the photograph could be used for educational purposes and on the museum's busy website. They told him there are pictures of the school Peter attended in Amsterdam, and they might now be able to pick him out.

The photo will soon be on display on the Anne Frank House website, and perhaps at the House itself, but the story is not quite complete. We know of Anne Frank's fate - arrest and then deportation to Auschwitz and Bergen-Belsen; she died of typhus in late February or early March 1945, only a few weeks before the camp was liberated. Of those in hiding with her only her father survived, and until his death in 1980 he dedicated his life to the protection and promotion of her diaries.

But the fate of Peter Schiff is less certain. He too must have spent many months in hiding, and upon capture it is believed he disobeyed orders to join an enforced labour unit in Amsterdam (the fate of his mother is unclear). Classified as a criminal, he was transported to the Westerbork transit camp near the Netherlands' northeastern border (the Frank family was also held there for a while), and from there to Bergen-Belsen and probably Auschwitz. The date of his death is unknown, although it is entered in the record books on 31 May 1945.

In place of Peter Schiff's final details we have something quite as valuable. Not just a photograph but also a love story, between a famous girl and a handsome boy, and an elderly man and his memories of a fractured childhood. 'We tried to make some very silly jokes,' Mic Michaelis says of the day he obtained his unique memento and said goodbye to a friend he would not see again. 'But instead of laughing, all we could do was to try not to cry.'