In 2016, Horton upset Sun to win men's 400m freestyle gold at the Rio Olympics. Horton clocked 3 minutes 41.55 seconds, eclipsing Sun by just 13 hundredths of a second at the Olympic Aquatics stadium.

The Australian swimmer previously dubbed his Chinese rival a dope cheat. Sun served a three-month ban in 2014 after testing positive to a banned substance. He said he unwittingly took the drug as part of treatment for a chronic heart problem.

In 2017, Sun took a sweet revenge by clocking 3 minutes 41.38 seconds, finishing 2.47 sec ahead of second-place Horton at the World Aquatics Championships.