Horton celebrated a "win for the good guys" after a surprise 400 metres freestyle victory over Sun at last year's Olympic Games in Rio de Janeiro.

Sun had served a secret three month ban for doping in 2014 after a failed test for banned stimulant trimetazidine.

He had returned to competition before news of the suspension emerged.

The two are due to meet again today as swimming action begins at the International Swimming Federation (FINA) World Aquatics Championships. 

Horton's comments generated huge controversy on social media last year from Chinese fans to the extent that Australian Olympic officials blocked his account to protect the now 21-year-old.

Hee insisted he does not regret his comments.

"I think I would still do the same thing, even if I knew the outcome," he was quoted as saying by The Australian.

"I don’t think it changes anything.

"I don’t know if it’s a rivalry [between us]. 

"I think it’s a rivalry between clean athletes and athletes who have tested positive, but there should be some good racing."

Horton has also criticised the decision to add the men's 800 metres freestyle onto the Olympic programme for Tokyo 2020.

The event, along with the women's 1,500m and a mixed medley relay, were approved by the International Olympic Committee (IOC) Executive Board last month to take the total number of aquatic medal events to 49.

Horton is due to compete over 400m, 800m, 1,500m and the 4x200m freestyle relay here this week but insists this schedule is too much for an Olympic Games.

"I think the 1,500 should have been in for women a long time ago," he said.

"I think we should all be swimming 1,500, but the 800 doesn’t really make sense.

"For the [pure] 1500 swimmers the 800 is good, but for the 400-1,500 swimmers, when you already have a massive week, it makes it a bit more difficult. 

"I don’t rate it as an event at the Olympics because the 1,500 is the pinnacle distance event.”

Horton warned that it may lead to athletes choosing between the 400 and 1,500m and thus reduce the quality of each event.

Doping issues are dominating the build-up to the World Championships.

This has once again centred around controversial Russian breaststroke star Yuliya Efimova.

Efimova was only granted permission to compete shortly before Rio 2016 by the Court of Arbitration for Sport after being initially barred due to an IOC rule banning Russian athletes who had served doping suspensions.

The four-time world champion was banned for 16 months in 2013 after failing for the anabolic steroid hormone Dehydroepiandrosterone - or DHEA - the previous year. 

She also tested positive in 2016 for meldonium, but was cleared of wrongdoing by FINA due to a lack of proof over whether she had taken the substance before or after it was banned on January 1. 

Efimova has further fuelled the flames in recent weeks by releasing a range of signature T-shirts, including one which bears the slogan "Go to CAS".

She has also posted on Facebook yesterday that she had undergone her 15th drug test of the year.

The 25-year-old is expected to resume her rivalry with American Lilly King, who repeatedly criticised her during Rio 2016 and claimed it was "incredible to win clean" after a 100m breaststroke victory.