The allegations emerged in January in The Sunday Times  but the reigning Olympic 200 metres freestyle champion denied wrongdoing and avoided punishment from FINA and its doping panel, instead receiving a warning.

The World Anti-Doping Agency (WADA) has since filed an appeal against this decision at the Court of Arbitration for Sport (CAS).

If CAS rules in WADA's favour, Sun could receive a lifetime ban, having already served a three-month suspension in 2014 after testing positive for prohibited substance trimetazidine.

Sun shrugged off the controversy surrounding him as he delighted the home crowd at the Guangdong Olympic Sports Centre with dominant performances in the men's 200m and 400m freestyle. 

The 27-year-old won the 200m in 1min 46.12sec, finishing ahead of Lithuania's Danas Rapsys in 1:46.28 and compatriot Wang Shun in 1:48.08.

Sun recorded a time of 3:42.75 in the 400m – the quickest time posted this year – to beat nearest opponent Gabriele Detti of Italy, who finished in 3:46.45.

Australia's Jack McLoughlin was third in 3:47.89.

In other races, three-time Olympic champion Katinka Hosszú added two gold medals to the one she claimed in the women's 400m freestyle yesterday.

The Hungarian swimmer won the 200m backstroke in 2:09.05, before securing the 200m individual medley in 2:08.72.

Sweden's Sarah Sjostrom finished the weekend with four golds, triumphing today in the 100m freestyle with a time of 52.82 and the 50m fly with 25.55.

Today's action concluded the inaugural FINA Champions Swim Series event, launched in response to the International Swimming League (ISL) and which has promised greater prize money for athletes.

“What a wonderful weekend of swimming," said FINA President Julio Maglione. 



"FINA is delighted at the success of this first leg of the FINA Champions Swim Series. 

"Feedback received from the athletes competing or attending the inaugural meet was very positive. 

"Only four months have passed since the Series was announced, and in that time FINA has shown how to turn ambitious plans into reality, serving swimmers and fans alike."

Despite the claims of positive feedback, the competition is viewed as a direct response from FINA to criticism from athletes who were allegedly barred from taking part in new ISL competitions.

The ISL have accused FINA of copying their competition model.

The next event will take place in Budapest from May 11 to 12.