Kristof Milak shattered Michael Phelps' long-standing world record in the 200 metres butterfly at the World Aquatics Championships in Gwangju on Wednesday.
Hungarian teenager Milak won the final in 1:50.73, breaking the previous record of 1:51.51, set by Phelps in 2009.
American great Phelps, who holds the record for the most Olympic gold medals having won 23 in his decorated career, had held the world-leading time in the event for 18 years in total, having become the youngest male to break a swimming world record at the age of 15 in March 2001.
Chad le Clos, who eventually finished third behind Daiya Seto and Milak, touched first through 50m and 100m, but the Hungarian stormed back to take the gold and break Phelps' decade-long record.
"It's a tremendous honour to beat such a great men's world record," Milak said in quotes published on the Olympic Channel's website.
"When I turned back and I saw the time, 1:50.73? All the pressure and tension just went off my back and all the joy came out."