Damiano David, the flamboyant singer of Italy's Eurovision-winning rockers Maneskin, has tested negative for drugs, contest organisers said on Monday.
The red lederhosen-clad vocalist was tested after footage of him leaning over a table in the hospitality area of the competition in Rotterdam went viral.
Eurovision, the annual televised pop music extravaganza watched by millions each year, is put together by the European Broadcasting Union.
The union, in Geneva, said that after claims of drug use backstage, it reviewed the facts, including checking all available footage.
It said David voluntarily had a drug test on Monday "which has returned a negative result seen by the EBU".
"No drug use took place in the green room and we consider the matter closed," the organiser said.
"We are alarmed that inaccurate speculation leading to fake news has overshadowed the spirit and the outcome of the event and unfairly affected the band."
Maneskin, the favourites, fought off heavy competition from France and Switzerland, surging to victory on Saturday with the public vote to win on 524 points with their song Zitti E Buoni.
"We wish to congratulate Maneskin once again and wish them huge success," the union said.
"We look forward to working with our Italian member Rai on producing a spectacular Eurovision Song Contest in Italy next year."
Such was the furore that even the French government weighed in, seeing grounds for disqualification if David tested positive.
France's European affairs minister Clement Beaune had called for "total transparency".
"I think there needs to be no doubt here," Beaune told RMC radio.
"If there is a problem, there are penalties. Provisions are made for sanctioning measures, including potential disqualification in case of problems."
French hopes had been riding high on singer Barbara Pravi, who was a favourite to end France's 44-year Eurovision drought with her moody ballad Voila.
But Pravi was edged out at the last minute by a surge in public votes for Maneskin.
"I don't want to be a sore loser," Beaune said. "In terms of image, we can't let people think that such competitions can result in such behaviour."
But the president of France's public broadcasting group said on Monday that the country would not contest its second-place finish, regardless of the speculation.
David was asked about the footage early on Sunday, and said he was looking down because guitarist Thomas Raggi had broken a glass.
"I don't use drugs. Please, guys. Don't say that really, no cocaine. Please, don't say that," he said.
The four-piece band, which also features bass player Victoria De Angelis, guitarist Raggi and drummer Ethan Torchio, told fans on Twitter: "We still can't believe what's going on. These last few days have been incredible and this is just the beginning.
"Our new album Teatro D'Ira has just gone platinum, and so has Le Parole Lontane. This is all thanks to you.
"We can't wait to go on tour all around the world and share our music with all of you."
Italy is one of Eurovision's "Big Five", along with Britain, France, Germany and Spain, who automatically qualify for the finals each year.
Meanwhile Britain's crushing "nul points" was down to the poor selection process, not bad blood over Brexit, a senior minister insisted on Monday.
James Newman scored no points from the jury or public vote for his song Embers.
It was only the second time the country has failed to win any points at all. The last time it happened was in 2003 after an off-key performance by the group Jemini.
But Saturday's poor showing was the second year in a row that Britain came in last place.
"There is a fundamental problem with the way that we are choosing our performances and singers," international trade minister Liz Truss told LBC radio.
But Truss dismissed a suggestion that voters passed over the UK entry because of the divisive departure from the EU.
"I don't think it's a post-Brexit snub," she said. "I think that we need to have more competition to get the right entrant."