China's three-time Olympic champion swimmer Sun Yang, who is banned until June 2024, on Friday saw his final appeal against a doping sanction dismissed, the Swiss Federal Court announced.

The punishment handed down by the Court of Arbitration for Sport (CAS) was "not contrary to the fundamental principles of the legal order", and Sun Yang's right to be heard "had not been violated", the Swiss Court ruled.

CAS banned Sun in June last year for refusing to give a sample to doping inspectors.

At the end of a long-running and controversial case, the Lausanne-based court reduced its original ban of eight years after Sun, 30, appealed to Switzerland's federal court over alleged bias.

The new ban of four years and three months, backdated to February 2020, ruled the 1,500m freestyle world record-holder out of the Tokyo Olympics and the 2022 Asian Games in his home city of Hangzhou.

Sun, who was banned for three months in 2014 for a separate doping offence, will be eligible to return in time for the 2024 Paris Games, although he will be 32 by then.

The swimmer, who has been dogged by controversy throughout his career, has always maintained his innocence in the murky events of September 2018 when doping inspectors visited his home.

The 11-time world champion said the testers were not qualified or authorised.