WUHAN, Oct. 26 (Xinhua) -- When Military World Games' naval pentathlete Gustaf Wahlberg of Sweden, who is 38 years old now, took swimming training at Sodertorns SS in his mid-20s, he would sometimes race against a 13-year-old girl.

It was after the girl, 12 years his junior, beat him one time in the pool that he decided to put an end on his career as a swimmer, who had focused training on freestyle and butterfly, after years of race.

Little did Wahlberg know back then that while his competition days in the pool were over, his young opponent would one day be crowned Olympic champion.

That young girl was none other than Sarah Sjostrom, now 26, the winner of three Olympic medals - one of each colour - 16 world championship medals, eight of them gold, and numerous continental championships. She has also broken four world records over 50m and 100m freestyle and 50m and 100m butterfly.

Sjostrom claimed her first European senior title at the age of 14, around about the time she was helping to bring the curtain down on Wahlberg's swimming career.

"Sarah and I come from the same club," said Wahlberg, who helped Sweden to a sixth-place finish in the naval pentathlon team event on Friday and came 21st in the individual event.

"She is 12 years younger than me so when she was like 13, 14 and I was coming to the end of my career (in swimming), we used to swim against each other.

"And she beat me. She did. So I thought 'maybe now it is time to stop'. She is really awesome," he said.