Russian teenage figure skater Kamila Valieva tested positive for a banned substance, Beijing Olympics testers confirmed Friday, while American snowboarding legend Shaun White finished an agonizing fourth in his final appearance.

After concerns about COVID-19, human rights and man-made snow in the build-up to the Olympics in the Chinese capital, doping became the latest controversy to rock the Games.

Reports of doping had swirled around the prodigious 15-year-old Valieva after the medals ceremony for the figure skating team event – in which she played a starring role to lead Russia to gold – was delayed this week.

On Friday, soon after she was seen practicing on the ice in Beijing, the International Testing Agency (ITA) confirmed traces of the banned substance trimetazidine were found in a sample she gave in December.

Valieva now faces a fight to stay at the Games and take part in the women's individual event, which starts on Feb. 15 and for which she is the favorite.

Her case will be decided by the Court of Arbitration for Sport (CAS) before then.

It is just the latest doping scandal surrounding Russian athletes in recent years at Olympic Games.

Russian competitors are taking part in Beijing as the Russian Olympic Committee (ROC) after the nation was banned because of a massive state-sponsored doping scheme at the 2014 Sochi Olympics, which it hosted.

"Such cases are not helpful to the Games," said International Olympic Committee (IOC) spokesperson Mark Adams on Friday, as the Games reeled from yet another doping scandal.

Former World Anti-Doping Agency (WADA) director Rob Koehler criticized his former agency, as well as IOC and CAS for not taking a stronger stand when they allowed Russia to compete in Olympics under a different name.

"By not banning Russia for four years, there was no need or desire for cultural change by Russian authorities ... By allowing Russia a free pass these organizations have severely let down every single athlete in Russia because it’s business as usual.

"Athletes in Russia deserved a cultural change, they deserved the right to have the opportunity to compete clean, instead WADA, IOC and CAS favored the power and influence of Russian sport over clean sport.

Russia's Olympic Committee said that Valieva had the right to compete in Beijing and that her team gold medal should stand.

Tearful farewell

For the second day in a row it overshadowed the action on the snow and ice at the Olympics, where an emotional White ended his storied snowboarding career by coming an agonizing fourth in the halfpipe, just missing out on a farewell medal.

The three-time Olympic champion from the United States is 35 now and nearly twice the age of some of his rivals.

"It's been a journey, I'm just so happy and thank you all from the bottom of my heart," said a tearful White.

"A lot of emotions are hitting me right now, the cheering from the crowd, some kind words from my fellow competitors at the bottom, I'm so happy.

"Snowboarding, thank you. It's been the love of my life."

Japan's Ayumu Hirano, who twice has had to settle for silver, wowed the crowd with a series of gravity-defying tricks to take a dramatic first place with a score of 96.00.

In alpine skiing, Switzerland's Lara Gut-Behrami added Olympic super-G gold to her world title. Mikaela Shiffrin finished ninth but was relieved just to get to the finish after flunking her first two events.

"I had no strategy at all," said Gut-Behrami, who timed 1:13 for victory. "I just tried to ski."

Shiffrin, a double gold medalist in previous Games, struggled between the first two intermediaries and eventually came racing through the finish line 0.79 seconds off winner Gut-Behrami's pace.

It was the first time the U.S. ski star had finished a race at these Games after she produced two unusual mistakes in the slalom and giant slalom this week, skiing out early in both.

"There was nothing sad about today, it's really solid skiing and everything was pretty much on point," said an upbeat Shiffrin, one of the biggest names at the Games.

She added: "I skied strong and it's a really big relief to be here now in the finish ... that's really nice for my heart to know that it's not totally abandoning everything I know about the sport."