A time od 46.40 was posted by the Chinese swimmer, but his record is already being called into question due to the doping scandal that emerged in China just months ago.
Last April it was discovered that 23 swimmers tested positive for substances incompatible with top competition. While WADA (World Anti-Doping Agency) were aware of it, more than half of them were able to participate in Tokyo.
The result saw China win six medals, four of them gold. China claimed that the result came from food contamination, something that WADA accepted despite the fact no evidence was presented.
Pan was not among the list of 23 athletes and he maintains that he has been closely monitored in recent times, never testing positive.
The swimmer smashed his own record, lowering it by four tenths from his February time, something Australian coach and former Olympian Brett Hawke believes is "humanly impossible."
The swimmer, who competed in the Sydney and Athens Games, considers himself an expert in the matter and said: "I have studied them for thirty years, I have studied that sport, the speed...it is not real".
The trainer claimed that it is impossible to lower a record that much in such a short time and that the Chinese swimmer won the race with unusual dominance.
"You can't beat a pack like that, with a body length lead. They are the best in history. It's humanly impossible," Hawke claimed on Instagram.
Everyone dopes.