France's Leon Marchand smashed Michael Phelps's last remaining world record on Sunday, winning the men's 400m individual medley at swimming's world championships in Japan.

Marchand clocked 4min, 02.50 -- more than a second faster than Phelps -- to finish ahead of American Carson Foster in 4:06.56 and Japan's Daiya Seto in 4:09.41.

Marchand is set to be one of the faces of next year's Paris Olympics and he warned that "the best is yet to come".

"It was insane," the 21-year-old said.

"That was one of the most painful things I did. That was amazing to do it here. The time is crazy."

Phelps's record of 4:03.84sec had stood since the 2008 Beijing Olympics and was the longest-held world record in swimming.

Second-place Foster said it was "pretty cool" to watch Marchand break it.

"Obviously the goal is always to win and Leon is a great competitor," said Foster.

"Being the closest person to history was pretty cool, getting a front-row seat to that."

Marchand, who is coached by Phelps's former mentor Bob Bowman, swam the second-fastest 400 IM ever at last year's world championships in Budapest, coming home in 4:04.28.

The Frenchman insisted on Saturday that breaking the record was just "a step in my journey".

amk/pbt