Gwangju - Australian relay world-record holder Shayna Jack denied wrongdoing on Saturday after she failed a drugs test and was forced to miss the swimming world championships in South Korea.
The 20-year-old, part of Australia's 4x100m freestyle team that set a world record at last year's Commonwealth Games, failed an out-of-competition test late last month and has been suspended, Swimming Australia said.
The first positive test related to the Gwangju world championships is embarrassing for Australian swimming after Olympic champion Mack Horton's protest against Chinese rival Sun Yang in Gwangju over salacious claims he smashed vials of blood following a test last year.
Jack, who returned home days before the start of the world championships in South Korea citing "personal reasons", denied deliberately taking a banned substance.
"I did not take this substance knowingly," Jack posted on Instagram.
"Swimming has been my passion since I was 10 years old and I would never intentionally take a banned substance that would disrespect my sport or jeopardise my career."
But American Lilly King savaged the swimmer later on Saturday.
"She's a drug cheater," sniffed the Olympic champion. "She has tested positive on a drugs test - doping is doping."
Australian officials ushered Jack back to Australia from a world championship training camp in Japan after the results of the June 26 test and gave her a provisional suspension, Swimming Australia said.
"Swimming Australia is and always has been committed to a clean sport," CEO Leigh Russell said in a statement.
"We have consistently supported a zero tolerance approach to doping and have been strong supporters of a rigorous and consistent approach to drug testing both here and overseas."
Australia's Horton took a highly visible stance when he snubbed Sun at a medals ceremony, provoking a furious reaction from China's 11-time world champion, who accused him of "disrespecting China" by not stepping on the podium.
Britain's Duncan Scott copied Horton after Sun retained his 200m freestyle title and several swimmers, including King and fellow Olympic champion Adam Peaty, spoke out in support of the two.
But Sun's coach Denis Cotterell slammed his fellow Australians for "double standards", noting Horton's Australian teammate Thomas Fraser-Holmes was banned by FINA for 12 months for missing a trio of drug tests.
Jack's failed test will now supply Sun and China with plenty of ammunition to shoot back.
Relay team mate Cate Campbell said: "I had absolutely no knowledge of this before tonight. We stand for a clean sport and I think the fact that Shayna isn't here strengthens that stance."
Russell expressed sadness at Jack's failed test.
"As you would expect, we are bitterly disappointed with allegations a swimmer has a prohibited substance in her system although it is important to point out that the matter is yet to be determined," she said.
"We will continue to provide appropriate support for Shayna. Our organisation will continue to reaffirm our zero tolerance approach."