THERE is plenty of evidence controversial Chinese swimming champ Sun Yang has an Olympic-sized attitude problem but as for him being a drug cheat, the case is much less clear cut.

Sun exploded to prominence at the 2010 Asian Games by coming within a second of beating the longstanding 1500m world record held by Grant Hackett — Mack Horton’s childhood hero.

He went on to smash that record by eight seconds at the 2011 world championships in Shanghai before clinching 1500m freestyle gold at the 2012 London Olympics. He also won gold in the 400m freestyle and tied for silver in the 200m freestyle.

Horton sledged Sun as a “drug cheat” before beating him for gold in the 400m Olympic freestyle final on Saturday.

The basis of Horton’s sledge stems from a three-month ban imposed on Sun by the Chinese Swimming Association in May 2014 after he tested positive for the stimulant trimetazidine.

The association opted for a lenient punishment after accepting Sun’s claim he had been prescribed the drug for a heart condition and that he had been unaware it had been added to the World Anti-Doping Agency’s (WADA) banned list less than five months earlier.

A firestorm erupted after it emerged that CHINADA (Chinese Anti-Doping Authority) did not report the failed test or the subsequent ban until after it had been served.

As a result, the 24-year-old’s numerous record-breaking performances were called into question; he was stripped of his win in the 1500m freestyle at the Chinese nationals and even banned from training in Australia.

The medication Sun received containing trimetazidine was for a heart muscle condition known as angina pectoris, which loosely translates from the Latin as “strangling feeling of the chest”, and can cause chest pain and palpitations.

Sun’s doctor, Ba Zhen, was slapped with a one-year ban from sport.

To muddy the waters further, on January 1, 2015, WADA reclassified and downgraded trimetazidine from a “stimulant” to a “metabolic modulator”.

THE HEART CONDITION IS REAL

Last year Sun’s medical condition came back to haunt him, with heart palpitations and chest pains forcing his last-minute withdrawal from the 1500m freestyle final at the 2015 World Championships in Kazan, Russia.

Italy’s Gregorio Paltrinieri won the gold in his absence and Connor Jaegar of the US got the silver.

“First of all, I am very sorry that I couldn’t swim the 1500m final,” Sun said in a press conference. “After the 800m competitions, I didn’t feel well in my heart. I felt uncomfortable in the warm-up tonight so I had to give up the idea of competing.

“I made the decision by myself and didn’t tell my coaches, as I said I am very sorry.

“After the warm-up, and while I was preparing to take part in the competition, I realised I just couldn’t compete. I didn’t see what time it was.”

EVERYONE THINKS HE’S A JERK

Sun’s fellow competitors were unsympathetic to his plight, given his reputation for being an aggressive disrupter during training sessions.

American swimmer Connor Jaegar, who went on to win silver at the race after Sun’s no show, told reporters he assumed Sun was simply screwing with his fellow competitors.

“I didn’t want to get my hopes up, but he wasn’t there and I was like, ‘Oh, he is probably just messing with us or something like that’,” Jaegar said.

“Standing up on the blocks and he still wasn’t there I was thinking, ‘Wow, is this really happening’.

“I hope he is not sick or injured and is OK.”

It later emerged that Sun had a meltdown while watching the final on TV in the locker room.

A Danish swimmer, who did not wish to be named, told Reuters in an email that there had been a “huge commotion” with the Chinese delegation and that Sun had been “agitated” watching the race go on without him.

Horton has said that Sun had tried to break his concentration by “splashing water” at him during training sessions, and he’s not the only swimmer to report a run in with the Chinese champion.

Brazilian coach Alberto Pinto da Silva accused Sun of assaulting female swimmer Larissa Oliveira as the pair warmed up during last year’s world championships.

“He was warming up and he pulled the Brazilian girl’s foot, Pinto da Silva said in a report submitted to world swimming body FINA.

“He ran her over. She got angry and had it out with him. He tried to elbow her and kick her. So then the Brazilian coaches went to speak to him. He said she was bothering him and one of the coaches said that the pool wasn’t just his. Everyone was at the side of the pool, and they were all swearing at each other.”

The Brazilian coach conceded that while there were verbal exchanges, there was no physical altercation during the incident.

“The Canadian (coach) came over to me and said, ‘he has already bothered my swimmers’,” Pinto da Silva said.

“The South African [coach] said he bothered the swimmers when they were swimming. Chile, Argentina, everyone came to tell me what to do. If he’s doing that to everyone then he’s a dangerous guy, he has no place in sport.”

HE CAN’T KEEP OUT OF TROUBLE AT HOME EITHER

In February 2013, Sun was formally criticised for his behaviour at a press conference held by the Zhejiang Institute of Sport.

It enforced a raft of disciplinary actions, temporarily banning him from any business-related activities after a series of articles appeared in the Chinese press about Sun’s relationship with his girlfriend.

Flight attendant Nian Nian, who had been kept a secret, was outed by social media users.

Sun angered swimming officials, who believed the relationship was detrimental to Sun’s performances in the pool, after posting pictures of the pair to social media site Weibo.

“Aside for a reported love affair with an air hostess making headlines very recently, Sun has systematically been skipping training sessions and instead has indulged in commercial activities for over 40 days,” China’s state run news agency Xinhua said.

The affair led to a fallout with his coach Zhu Zhigen, resulting in missed training sessions.

In November that year, Sun was caught driving without a licence after crashing his friend’s Porsche into a bus while driving in Hangzhou. He was jailed for a week and fined 5000 yuan.

Days later, the State General Administration of Sports announced it was temporarily banning Sun from any business-related activities, the national team swimming camp and any competitions.

It lifted the ban in April 2014 on grounds of “good behaviour”.

By this time, however, Sun had been banned for three months after testing positive for trimetazidine and Zhu had resigned — citing health concerns of his own.

Attempts by Sun to reconcile with Zhu have failed.