China's world and Olympic swimming champion Sun Yang served a three-month ban earlier this year after testing positive for a banned stimulant, the China Anti-Doping Agency (CHINADA) said on Monday.
The agency said Sun had tested positive for trimetazidine, a substance normally used to treat angina. The stimulant was added to the World Anti-Doping Agency's (WADA) banned list this year.
"I have taken many doping tests during years of training and competition and I had never failed one before," Sun told China's official Xinhua news agency.
"I was shocked and depressed at that time, but at the same time it made me cherish my sporting life even more. I will take it as a lesson and be more careful in the future."
CHINADA said Sun tested positive in May during the national swimming championships and although the result was "not very serious" it still warranted a penalty.
Sun was also fined 5,000 RMB ($816) (522 pounds) while officials from his provincial swim team were also handed unspecified penalties.
“Sun Yang in this matter was not completely responsible and the positive test is his mistake, but the mistake is not very serious or negligent," CHINADA deputy director Zhao Jian said.
"Because of this, the three-month ban is reasonable."
Xinhua said Sun had waived his right to have his 'B sample' tested but had defended himself at a hearing in July, saying he had been prescribed the drug for heart palpitations he has suffered since 2008 and was unaware that it was recently banned.
Trimetazidine was added to WADA's banned list, which is updated annually, in January this year as an "example to reflect emerging patterns of drug use."
'Huge bad news'
Sun served his suspension in time to represent China at the Incheon Asian Games in South Korea in late September, where he won three gold medals.
He did not mention the suspension in Incheon and CHINADA said it did not immediately announce the sanction because it only reveals positive tests every three months.
"Sun is the most famous athlete in China and is known in the world, which means we need to handle his case very cautiously. This is huge bad news but we will not cover it up," said Zhao.
"We announce positive cases and test statistics in our quarterly reports just as WADA requires."
Sun burst into the international spotlight when he won the 400m and 1,500 freestyle events at the London Games in 2012, becoming the first Chinese man to win Olympic swimming gold.
The 22-year-old has also won five world titles, holds the world record for 1,500m, and is one of China's best known and controversial sportsmen.
In early 2013 he was suspended from engaging in commercial activities after missing training and breaching team rules.
Later that year he was ordered to spend a week in a detention centre after crashing a car that he had driven without a licence.
China's swimming authorities slapped a blanket suspension on him, banning him from all training and competition, before he made his return at the National Championships.
