Budapest - Sarah Sjostrom of Sweden became the first woman to win four golds in the women's 100m butterfly following her victory in Monday's final at the world championships.
The 23-year-old clocked 55.53 seconds, a new championships record, just 0.05sec from her own world record set at the Rio de Janeiro Olympics last year.
She is the first reigning Olympic champion to add the world title in the event.
Australia's Emma McKeon took silver at 0.65sec back with Kelsi Worrell taking bronze at 0.84.
Sjostrom broke the 100m freestyle record on Sunday when she became the first woman to swim under 52 seconds.
Sjostrom first won the 100m butterfly title as a 15-year-old at the 2009 championships in Rome.
She failed to defend it in 2011 in Shanghai, but took gold again at both the 2013 championships in Barcelona and then again two years ago in Kazan.