They say if it sounds too good to be true it probably is. So when news surfaced in Germany of a promising young luger from the tropical islands of Tonga who bore the same name as a racy German underwear firm with a dream of sledding to victory at the Olympics, scepticism might well have been warranted.

But the story was too delicious. Bruno Banani, 24, ostensibly the son of a coconut farmer from the South Pacific nation, was aiming to be Tonga's first ever competitor at a winter Olympic games. In doing so, went the story, he was fulfilling the wish of the Tongan Princess Royal, Salote Mafile'o Pilolevu Tuita, whose life's ambition was to see a citizen from her sun-drenched isles triumph among the ice and snow of the world's premier cold weather sporting contest.

When Banani, whose catchphrase was "coconut powered", was unveiled to the German media, he was naturally sponsored by Bruno Banani, a purveyor of knickers and bras from the east German city of Chemnitz.

But he seemed legit. After all, he had been invited to train with the world-beating German luge team. They had apparently taken pity on the Tongan, whose upbringing on the resolutely snowless islands had not best prepared him for a lifetime of hurtling feet-first down a treacherously slippery track at 80mph. It was like the film Cool Runnings which was about Jamaica's first bobsled team trying to make it to the Olympics. But now an investigation by Der Spiegel magazine has revealed that the plucky luger really was too good to be true – not in fact christened Bruno Banani by his mother, but by some mischief-making opportunists at a marketing company in Leipzig.

According to Spiegel, certain elements of the Banani story are true. He is indeed 24 and until his move to Germany was one of the 106,000 inhabitants of Tonga. He did attend a "casting" session on the islands in 2008, hosted by the German luge champion Isabel Barschinski. And yes, the Princess Royal did actually dream of getting a Tongan to the Winter Olympics.

But it's here that the Banani myth starts to become detached from reality. It seems that the young IT student who was picked for luge success was actually called Fuahea Semi and was not the son of a man who farmed coconuts, but cassava. At this point a marketing firm called Makai came into play, according to Der Spiegel. At the final selection round in Tonga, it intervened and somehow arranged for a passport to be issued for Semi in the name of Bruno Banani.

And, presumably reasoning that most people hadn't heard of cassava, it rewrote his father's history so that he farmed coconuts instead.

The Guardian contacted Mathias Ihle, the boss of Makai Europe, to see if everything Spiegel reported was true, and ask for an interview with Banani/Semi. In an emailed response, Ihle thanked us for our interest and said that with regret, his client would not be available for an interview.

"Bruno is about to compete at the luge world championships [held in Altenberg, east Germany, from 6 February] and we are trying to make things as calm as possible around him, especially after the [Spiegel] article. Unfortunately I cannot help you further," wrote Ihle. Norbert Loch, the trainer of the German national luge squad, did not respond to inquiries.Whether the International Olympic Committee, which has very strict rules about sponsorship, allows Banani to compete at the 2014 olympics in the Russian city of Sochi remains to be seen. Although it may not come to that: when Banani tried to qualify for the 2010 Vancouver games, he crashed out and ended up in hospital with concussion.