Even legends' records are meant to be broken.

And Sunday, the last of Michael Phelps' individual swimming records finally fell as Leon Marchand, a 21-year-old Frenchman set the world record in the men's 400-meter individual medley.

Marchand cruised to the win in 4 minutes, 2.50 seconds at the world championships in Fukuoka, Japan, beating out Phelps' time of 4:03.84, which he set at the 2008 Olympics in Beijing.

World Aquatics @WorldAquatics

THIS IS UNBELIEVABLE 🫣<br>🇫🇷Leon Marchand beat the longest World Record in the books after 21 years!!!<a href="">@FFNatation</a> <a href="">#AQUAFukuoka23</a> <a href="">

He broke the record with Phelps in attendance and received his gold medal from the greatest swimmer of all-time.

"That was insane, one of the most painful things I've done," Marchand said following the race. "It was amazing to do it here, and the time is crazy."

"The best is yet to come," he added later.

Marchand has followed in Phelps' footsteps, training under US national team coach Bob Bowman at Arizona State University. He is setting himself up for a path of superstardom entering the 2024 Olympics in Paris where he'll be the hometown favorite.

And following his performance this weekend, all eyes will be trained on him as Phelps' potential successor.

"I think I can handle the pressure pretty well right now," Marchand said. "It's not perfect and I can get better and I have one year to improve."

Marchand has some massive shoes to fill as Phelps is the most decorated Olympian of all-time with a total of 28 medals.

Phelps previously held five individual world records in the 200m butterfly, 200m freestyle, 200m individual medley, 400m individual medley and 100m freestyle. After Sunday he is still a part of world records set by the United States in the 4x100 and 4x200 freestyle relays.