Germany was rocked by the revelations last night that Günter Grass, its greatest living author and doyen of the Left, was a member of Hitler's elite Waffen-SS. The Nobel laureate, who has been the country's moral guide for decades, admitted in an interview published today that he became a member of the infamous Nazi corps at the age of 17.

The 78-year-old said he was driven by feelings of guilt to reveal the details of his "shameful" past in his autobiography, Peeling the Onion, due to be published next month. "It was weighing on my mind. My silence over all these years is one of the reasons why I decided to write this book. I forced myself to do it," he told the Frankfurter Allgemeine Zeitung newspaper. Asked why he was breaking his silence after more than 60 years, Grass said: "It had to come out finally." He added: "It will stain me forever."

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He did not give any details as to whether he knew whether his division, the 10th Tank Division Fundsberg was involved in any atrocities, but claimed that he never fired a single shot. He stressed his youthful naivety, and his desperation to get out of the corps because he found it gruelling. "It was very hard. It was all there was. The only question you asked was: 'How do I get out of it?' So I infected myself with jaundice, but that only helped for a few weeks. Then the grind began again and an inadequate training with ageing equipment. In any case, I had to write about it." He said his feelings of guilt developed only in later years. "It was always combined with the question: 'Could you not have realised at that point what was happening to you?'"

Grass, the author of dozens of plays and 11 novels, the most famous of which, The Tin Drum, is an examination of wartime Germany, has long been seen as the embodiment of the German zeitgeist. Throughout his career he has famously criticised those unwilling to deal with Germany's Nazi past.