China's former 100m freestyle world champion and swimming pin-up Ning Zetao announced his retirement from the sport on Wednesday, his 26th birthday. Ning won the 100m free world title in 2015 and was a four-time gold medallist at the Asian Games a year earlier. But his career has been on the slide since and he hangs up his trunks with the reputation of a talent never fulfilled. Ning, who served a one-year suspension after testing positive for clenbuterol in 2011, announced his retirement on Weibo, China's equivalent of Twitter. "Don?t be afraid of the past and the future! Say good bye to the swimming pool and blue water and restart my own new life," Ning wrote."Thank you, my dear fans! I wish you all the best." He added in English: "The way to success is never easy, push yourself and DO NOT SETTLE."