China's Sun Yang, one of the world's premier swimmers, has been banned from competition for eight years for violating anti-doping rules, the international Court of Arbitration for Sport has ruled. The ban means the 28-year-old athlete will miss the 2020 Olympics in Tokyo — and it could very well end his career.

The Switzerland-based sports body said Friday that the three-time Olympic champion was guilty of a doping offense when he failed to cooperate with officials who tried to collect his blood for testing in 2018.

Sun, who won gold in the 200-meter freestyle in the 2016 Rio Olympics, said he would "definitely" appeal the ban, according to Xinhua.

"This is unfair. I firmly believe in my innocence," he said, according to the Chinese news agency. "I will definitely appeal to let more people know the truth."

The 6-foot-7-inch Sun is the world record holder in the 1,500-meter freestyle, which he broke at the 2012 Olympics in London. He is considered one of China's most popular sports figures and is the first Chinese swimmer to win Olympic gold.

He's also a polarizing figure in the sport. Chinese swimming officials banned him for three months in 2014 after he tested positive for a banned stimulant.

In a statement released Friday, the Court of Arbitration for Sport said that "the protocol adopted by the World Anti-Doping Agency for the conduct of doping controls, had not been properly followed" by Sun.

"The CAS Panel unanimously determined, to its comfortable satisfaction, that the Athlete violated Article 2.5 FINA DC (Tampering with any part of Doping Control)," it said.

The court held an open hearing on Sun's case in November.

According to news reports of the hearing, anti-doping officials made a visit to Sun's home to collect blood and urine samples in September 2018. It turned confrontational. A vial of Sun's blood was reportedly broken with a hammer.

The Olympic champion's mother instructed a security guard to break the casing around the container so that it was unusable for testing, The Associated Press reports.

According to The Wall Street Journal, the Sun family told the court that the container was not broken intentionally.

An initial investigation of what happened by FINA, the international swimming and diving body, found that Sun violated no anti-doping rules, China's swimming association said in January 2019.

Following that announcement, the World Anti-Doping Agency appealed to the Court of Arbitration for Sport, which issued the ban Friday. The court added: "the Athlete failed to establish that he had a compelling justification to destroy his sample collection containers and forego the doping control."

WADA said it welcomes the court ruling.

"WADA decided to appeal the original FINA ruling having carefully reviewed it and having concluded that there were a number of points that seemed to be incorrect under the Code," Oliver Niggli, the agency's director general, said in a statement. "Today's CAS ruling confirms those concerns and is a significant result."

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