Chinese swimmer Sun Yang has once again found himself at the centre of controversy at the 2019 world aquatics championships in Gwangju, South Korea.

Multiple competitors refused to acknowledge Sun on the podium, and the 27-year-old freestyle star clapped back when Brit Duncan Scott followed Australia's Mack Horton in refusing to shake Sun's hand. Sun responded by shouting at Scott, "I win, I win, you lose."

WATCH | Sun Yang gets snubbed yet again:

China's Sun Yang is once again shunned by a competitor on the medals podium, this time by Great Britain's Duncan Scott. Sun faces a lifetime ban if found guilty of smashing vials of his blood with a hammer during a clash last year with drug testers. 1:04

But how did we get here in the first place? Here's a timeline:

2012 London Olympics: Sun bursts onto the scene with the best Chinese Olympic swimming performance of all time. He hauls in a national-record four medals, including gold in the 400-metre freestyle and a world record in the 1,500, an event he outdistanced Canadian and silver medallist Ryan Cochrane by more than eight seconds. Sun also grabs silver in the 200 and helps China win bronze in the 4x200 freestyle relay. The relay medal represents China's first-ever team podium appearance.

2013 world championships: Sun shows he's here to stay. He wins gold medals in the 400, 800 and 1,500 to go along with the Chinese 4x200 win, in which he overcomes a two-second deficit as anchor by outracing American Ryan Lochte for gold. He becomes the second swimmer ever to win all three long-distance freestyle events at worlds.

May 2014: Sun is banned three months by the Chinese Swimming Association (CSA) after testing positive for trimetazidine, which was considered a stimulant at the time. The drug only helps in-competition, unlike some other performance-enhancing drugs like testosterone or human growth hormone that produce more long-standing gains. Sun claims he was prescribed trimetazidine for heart palpitations, but did not register the condition with swimming's governing body, FINA.

The substance was later reclassified from a stimulant to a "modulator of cardiac metabolism," though it remains banned. The CSA rules there was sufficient evidence of lack of intent, and while the World Anti-Doping Agency (WADA) admonishes the CSA for failing to report the ban until after it was served, it does not press further into the case.

2015 world championships: Another dominant showing for Sun produces gold in the 400 and 800 freestyle along with silver in the 200. However, he is forced to drop the 1,500 after claiming he had heart issues. "I feel very sorry that I couldn't be present for the 1,500," Sun tells reporters. "I didn't feel good in my heart. Today I felt really uncomfortable at the pool during my warm-up and I had to give up the idea of competing."

Later, Sun is accused of assault by the coach of Brazilian swimmer Larissa Oliveira. A spokesperson for Brazil refers to the encounter as "contact" but "not a fight." Sun is cleared of wrongdoing by FINA, the explanation being the warm-up pool was overcrowded, leading to incidental contact.

Sun swims in the 800 free at worlds. (Mark Schiefelbein/The Associated Press)

2016 Rio Olympics: Sun wins gold in the 200 free, making him the first swimmer ever to stand atop the Olympic podium in the 200, 400 and 1,500 events. But controversy follows Sun once again ahead of the 400, when Australian Mack Horton accuses him of splashing water in his face during practice as a distraction. After a Chinese denial, Horton responds by calling Sun a drug cheat multiple times.

China's Olympic organization then demands an apology from Horton that he refuses to give. Horton also receives plenty of derision from Chinese fans online, where's he's called a racist, a snake and disrespectful. The Chinese organization says Horton's claims damaged ties between the two countries, and adversely affected the image of Australian athletes.

September 5, 2018: Three people arrive at Sun's house claiming to be anti-doping testers. Sun, not trusting they are telling the truth, refuses to hand over a vial of blood. He eventually smashes the vial with a hammer, according to the Sunday Times. The popular British newspaper also reports Sun faces a lifetime ban over the incident.

FINA reviews an investigation launched into the incident by an independent inquiry panel, where it's determined that only one of the three people possessed proper accreditation. It says Sun noticed something was up, so he pressed further before calling the Chinese anti-doping centre asking what to do. The investigation says Sun determined not to trust the "testers" and destroyed the vial of blood. Because of the lack of accreditation, the panel concludes the vial could not be considered a sample, and therefore Sun could not be penalized. FINA accepts this explanation.

WADA, however, disagrees with FINA and sends the case to the Court of Arbitration for Sport, where it is still being reviewed. FINA has since been criticized for a lack of transparency by many swimmers, as well as the former head of Australia's anti-doping agency.

2019 world championships: Sun and Horton land medals in the 400 free, with Sun taking gold. At the medal ceremony, Horton refuses to stand on the podium alongside his Chinese rival because he doesn't believe Sun should be allowed to compete while the case remains under review. Horton is applauded in the lunchroom by his fellow swimmers for the decision.

WATCH | Mack Horton stages protest against Sun:

Australian Mack Horton refused to stand next to Chinese swimmer Sun Yang on the men’s 400-metre freestyle podium. Sun is currently facing allegations of doping rule violations that could result in a ban from the Tokyo 2020 Olympic Games. 0:59

A day later, Sun wins the 200 free after Lithuania's Danas Rapsys is disqualified for a faulty start. Britain's Duncan Scott ties for bronze, and follows Horton in refusing to acknowledge Sun. But this time, Sun claps back and appears to confront Scott, yelling "I win, I win, you lose." Scott receives praise for his move, including from teammate Adam Peaty.

The potential for more drama still exists, with the 1,500 final set for Sunday.