Chinese swimmer and triple Olympic champion Sun Yang won a huge victory seven months before the Tokyo Olympics with Switzerland's top court overturning an eight-year doping ban.
The 29-year-old - the first Chinese swimmer to win Olympic gold - will now have a chance to state his case again at a second hearing by the Court of Arbitration for Sport (CAS), based in the Swiss city of Lausanne, before the Tokyo games next year.
He is now free to compete until his case is heard again, meaning he could aim to defend his 200m title in the delayed Olympic games.
The swimmer is accused of destroying a blood vial with a hammer when collectors visited his home in September 2018 during an out-of-competition doping test.
The Swiss Federal Supreme Court said in a statement on Thursday that it had "approved the request by the Chinese swimmer Sun Yang for revision of the arbitral award of the Court of Arbitration for Sport (CAS) in Lausanne dated 28 February 2020... on the grounds of bias of one of the arbitrators of the CAS".
Sun's lawyers had previously accused CAS panel chairperson Franco Frattini of bias and putting out anti-China tweets.
"The award of the CAS is set aside. The CAS will have to render a new award in the case of Sun Yang in a different composition of the panel," the federal court said.
The ban had sent shockwaves through China's sporting world, given the 1500m freestyle world record-holder's stature in his homeland and the severity of the punishment was greeted with disbelief by his fans.
Sun, who has 11 world championships under his belt and won two golds at the 2012 London Olympics and one in Rio de Janeiro in 2016, had said in February he would fight the ban till the end and defended his action saying the doping testers who went to his home were not qualified.
Refused to share podium
"Let more people know the truth," said Sun.
"I believe in my innocence! Believe in the truth and defeat the lie!"
Sun also served a three-month doping suspension in 2014 for taking the stimulant trimetazidine, which he said he took to treat a heart condition.
The ban was not announced until after it ended and he never missed a major event.
Australian swimmer Mack Horton and Scottish swimmer Duncan Scott had refused to share a podium with Sun at the World Championships in South Korea in 2019, calling him a drug cheat.
Sun's lawyer Zhang Qihai said he would pursue a case against a sample collector who he said used "false proof."
"The 28th of February 2020 was a dark day," Zhang said in a statement.
The World Anti-Doping Agency said the move "upholds a challenge against the chair of the CAS Panel and as such has no bearing on the substance of the case".