Hungarian teenager Kristof Milak has shattered Michael Phelps' 10-year-old world record in the 200m butterfly.
Milak won gold in a time of 1m 50.73s at the world swimming titles in South Korea, lopping 0.78s off Phelps' 1m 51.51s set in Rome in 2009.
"It's a tremendous honour to set such a great record," he said.
"Until 14, I was a backstroker, and later, I focused on the butterfly. But earlier I only did 100 metres because I wasn't strong enough.
There can be no question about his strength now.
At 19, Milak is the youngest winner of the 200m butterfly since Phelps triumphed as an 18-year-old in 2003, the second of the American great's five world titles in the event
"When I turned back and saw the time, all the pressure, all the tension just got off my back, and all the joys came out," Milak said.
Chad le Clos of South Africa was out under world-record pace through the first lap before Milak gained the lead after 150 metres.
"Unbelievable race, really," said Le Clos, an old rival of Phelps. "Probably one of the greatest races ever."
Daiya Seto of Japan finished 3.13s behind for silver in 1m 53.86s Le Clos settled for bronze in 1m 54.15s.