Conspiracy of silence: Could the release of secret documents shatter Felix Mendelssohn's reputation?

Did Felix Mendelssohn's passion for the Swedish soprano Jenny Lind lead to his early death? If reports of a document buried in the bowels of the Royal Academy of Music are to be believed, a potentially devastating new light is waiting to be shed on the composer's life, his death and his music, on the eve of his bicentenary, which is sparking worldwide celebrations in 2009.

In 1896, Lind's husband, Otto Goldschmidt, allegedly placed in the archive of the Mendelssohn Scholarship Foundation (housed at the RAM) an affidavit in which – according to Professor Curtis Price, former principal of the RAM – he declares that he'd destroyed a letter that would have been deeply injurious to the reputations of his wife and Mendelssohn: an 1847 missive from the composer to the soprano declaring passionate love for her, begging her to elope with him to America, and threatening suicide if she refused. Lind, one infers, did refuse. Several months later, Mendelssohn was dead.

It has long been thought that Lind was in love with Mendelssohn, requitedly or not, but did not pursue it because he was married; but the plot looks thicker and more significant. Clive Brown's book, A Portrait of Mendelssohn, mentions papers in this archive "deposited in 1896 by Goldschmidt" that "tend to substantiate the notion of an affair" with Lind; were "to remain sealed for 100 years", were "said to have been opened in 1996", but "a conspiracy of silence surrounds their contents". The Foundation, which makes an award to a young composer every two years, was set up in Mendelssohn's memory in 1849 by Lind herself.

The Goldschmidt documents' content has never been made public – the "conspiracy of silence" continues. But Professor Price, who has viewed the affidavit himself, has spoken of its revelations, and is calling for "a full scholarly investigation".

Until now, Mendelssohn has been deemed the happiest of composers. The creator of such favourites as the incidental music to A Midsummer Night's Dream, the Violin Concerto, and the oratorio Elijah, he was the grandson of the Jewish philosopher Moses Mendelssohn. Born into a privileged family, he was a child prodigy, and went on to become a highly successful composer, conductor and educator. He was also gifted in painting and writing, enjoyed a happy marriage, and had five children. It has been thought that the only tragedies he experienced were the death of his sister Fanny in May 1847, followed by his own six months later, aged 38. But this may be far from the full picture.

He first met Lind on 21 October 1844. She was 24, an unaffected Scandinavian girl, untouched by the artificiality and glitz of the operatic world. "Did you meet her in private life, you would not notice her as a beauty," wrote her biographer, Charles G Rosenburg, about three years later. "She must be seen when her countenance is lighted up with the inspiration of her art, and then, possibly, you might pronounce her beautiful."

Mendelssohn was not the first to be bowled over: in 1843, on tour in Copenhagen, Lind met Hans Christian Andersen, and became the unrequited love of his life, inspiring his tale The Nightingale, hence her nickname, "The Swedish Nightingale". The composer, possibly infatuated, planned an opera for Lind on the Lorelei, the Rhine siren who lures men to their death. It was never completed, but Mendelssohn did write the soprano solo of Elijah for Lind. Friends, including Andersen and the pianist Clara Schumann, remarked on their attachment. An acquaintance who met Lind at the Mendelssohns' home in 1846, remarked: "She is such a fine and beautiful character. Yet she is not happy. I am convinced that she would exchange all her triumphs for domestic happiness. That sort of happiness she observes in Mendelssohn's home with his wife and children."

It's some way from there, though, to a plea for elopement and a suicide threat – and in 1847, Mendelssohn experienced a severe crisis. This has long been attributed to the death of his sister Fanny, to whom he was very close. But if Mendelssohn – already overwhelmed by the pressures of being director of Leipzig Conservatoire, conductor of the Leipzig Gewandhaus Orchestra, and loving husband and father – experienced not only the loss of Fanny but also an impossible love affair and subsequent rejection, the blow would have been huge.

Eye-witness accounts and medical reports into the composer's death all assert that he suffered a series of strokes. One could speculate that these could have been induced by self-administered poison, but that seems unlikely since Fanny, too, died of a stroke, and it ran in the family. Yet Mendelssohn's crisis could have precipitated his fatal haemorrhage, casting a horrible irony over his alleged suicide threat. Mourning Mendelssohn, Lind wrote: "[He was] the only person who brought fulfilment to my spirit, and almost as soon as I found him I lost him again." In 1869, she and Goldschmidt, a former student of Mendelssohn's whom she married in 1852, erected a plaque to Mendelssohn's memory at his birthplace in Hamburg. (The Nazis tore it down in 1936.)

The cellist Steven Isserlis is related to Mendelssohn: they share an ancestor in R Moses Isserlis of 16th-century Krakow, the grandfather of Moses Mendelssohn. The cellist alerted me to the existence of the mysterious papers, adding: "If he had committed suicide, the family would have covered it up." For him, it's obvious that his eminent ancestor was not all sweetness and light: "You can hear it in the music. His F minor String Quartet, for example, is extremely tormented."

The quartet was Mendelssohn's last major work. "The trouble is, people can't forgive him for being too much of a genius too young," Isserlis says. "Everyone loves to think of him as the happy, fulfilled composer. But there's a tragic side to his late works. I think he experienced a fundamental shift of personality in that last year."

The nature of Mendelssohn's music could be a giveaway even earlier. Its emotional content is high-impact, driven, with deeply romantic sensibilities, but almost always within contained classical forms. But it packs such an intense punch in terms of nervous energy, something probably had to give. Maybe Mendelssohn's greatest tragedy is that his music has been denigrated as shallow – mainly by anti-Semitic commentators such as Wagner – with his happy life cited as a pathetic excuse. Yet it's possible that his passionate, oversensitive nature drove him to what would have been a nervous breakdown, had he survived it.

On Isserlis's recommendation, I visited Professor Price, a trustee of the Mendelssohn Scholarship Foundation. He believes the affidavit's contents "should be published". It was not within his remit, though, to grant either me or Isserlis access to it, and our pleas to the Foundation met respectively with refusal and silence, despite Isserlis's family connection. One inevitably emerges speculating whether this indicates that there must be something to hide – especially since, if it's true that Goldschmidt put a 100-year embargo on the affidavit, that time elapsed 12 years ago.

Without that document, there can be no scholarly report of the type Professor Price advocates. And if the course of events proved true, its significance would not be restricted to Mendelssohn's private life. It could transform critical views of his music. Until then, we won't understand this glorious composer as fully as he deserves.