Sun Yang secured his first gold medal since his suspension on Sunday at the Chinese National Summer Swimming Championships, a second-tier event in his country.

Sun won the men's 400m freestyle, pulling away from his rivals after the first 200m to finish in 3:49.58, well off his personal best of 3:40.14, an Olympic record set at London 2012.

The freestyle specialist was originally suspended for eight years by the World Anti-Doping Agency (WADA) in 2020 for destroying blood vials during a test in 2018, a situation he continues to dispute.

The ban was reduced on appeal by the Court of Arbitration for Sport (CAS) in 2021 to four years and three months, which will expire in May 2024, too late for him to qualify for the Chinese team for the Paris 2024 Olympics.

Sun told state news agency Xinhua that he could have performed better. "I feel rusty in controlling the speed and I need more competitions," he said.

The swimmer, who was born in Hangzhou on 1 December 1991, posted on Chinese social media platform Weibo on Sunday, similar to the banned X, that his past victories and failures had "taught him how to face the many difficulties and challenges of life".

Sun's comeback follows intense scrutiny of Chinese swimmers overdoping allegations at the Tokyo Olympics, with concerns about doping continuing ahead of Paris 2024.

At London 2012, the six-foot-tall Sun became the first Chinese swimmer to win Olympic gold in the men's 400m and 1500m, setting a world record in the process. He was also the first swimmer from the Asian country to win gold medals at the World Championships in all freestyle distances from 200 to 1500 metres.

A three-time Olympic gold medallist and eleven-time world champion, Sun is the most decorated Chinese swimmer in history, but he is considered by many to be a cheat.

In September 2018, Sun was involved in a controversial incident during an out-of-competition doping test at his home. The Doping Control Assistant (DCA) lacked proper accreditation and took photos of Sun without his consent, leading him to refuse to give a blood sample. A security guard broke the container to prevent the testers from taking the vials.

FINA (now World Aquatics) ruled that Sun had not violated anti-doping rules due to the actions of the DCA, but in February 2020, CAS overturned FINA's decision and imposed an eight-year ban on Sun for manipulating the doping control process.

Some analysts suggested that the trial was marred by serious translation problems, conflicts of interest, bias and a "lack of evidence" regarding the Chinese swimmer's doping activities. In the end, CAS found no evidence of doping and allowed Sun to keep his medals, but suspended him for his conduct.

On 22 June 2021, following a new hearing, CAS upheld the ban but reduced it to four years and three months.

His successful career has been marred by suspicions from some rivals who labelled him a cheat at the 2016 Rio Olympics, and two competitors refused to stand on the podium with him at the 2019 World Championships.

Prior to this latest suspension, Sun also received a three-month ban in 2014 for testing positive for a banned substance.

Despite the criticism and the challenge of returning after a long absence, Sun continues to seek redemption and reaffirm his place in Chinese and world swimming history.