Swimming - 18th FINA World Swimming Championships - Men's 100m Backstroke Heats - Nambu University Municipal Aquatics Center, Gwangju, South Korea - July 22, 2019. Matt Grevers of the U.S. competes. REUTERS/Kim Hong-Ji 

Swimming – 17th FINA World Aquatics Championships – Men's 4x100m Medley Relay Final – Budapest, Hungary – July 30, 2017 – Matt Grevers and other members of the U.S. Team celebrate winning the race. REUTERS/Michael Dalder TPX IMAGES OF THE DAY 

Swimming – 17th FINA World Aquatics Championships – Men's 4x100m Medley Relay awarding ceremony – Budapest, Hungary – July 30, 2017 – Matt Grevers, Kevin Cordes, Caeleb Remel Dressel and Nathan Adrian of the U.S. (gold) celebrate on the podium. REUTERS/Bernadett Szabo 

Swimming – 17th FINA World Aquatics Championships – Men's 4x100m Medley Relay awarding ceremony – Budapest, Hungary – July 30, 2017 – Matt Grevers, Kevin Cordes, Caeleb Remel Dressel and Nathan Adrian of the U.S. (gold) celebrate on the podium. REUTERS/Michael Dalder 

Swimming – 17th FINA World Aquatics Championships – Men's 4x100m Medley Relay Final – Budapest, Hungary – July 30, 2017 – Matt Grevers and other members of the U.S. Team celebrate winning the race. REUTERS/Michael Dalder 

Swimming – 17th FINA World Aquatics Championships – Men's 50m Backstroke awarding ceremony – Budapest, Hungary – July 30, 2017 – Junya Koga (silver) of Japan, Camille Lacourt (gold) of France and Matt Grevers (bronze) of the U.S. pose with medals. REUTERS/Bernadett Szabo 

Swimming – 17th FINA World Aquatics Championships – Men's 50m Backstroke awarding ceremony – Budapest, Hungary – July 30, 2017 – Junya Koga (silver) of Japan, Camille Lacourt (gold) of France and Matt Grevers (bronze) of the U.S. pose with medals. REUTERS/Michael Dalder 

Swimming – 17th FINA World Aquatics Championships – Mixed 4x100m Medley Relay awarding ceremony – Budapest, Hungary – July 26, 2017 – Simone Manuel, Matt Grevers, Caeleb Remel Dressel and Lilly King of the U.S. team (gold) celebrate on the podium. REUTERS/Bernadett Szabo 

Swimming – 17th FINA World Aquatics Championships – Mixed 4x100m Medley Relay awarding ceremony – Budapest, Hungary – July 26, 2017 – Simone Manuel, Matt Grevers, Caeleb Remel Dressel and Lilly King of the U.S. team (gold) pose with the medals. REUTERS/Stefan Wermuth 

Swimming – 17th FINA World Aquatics Championships – Mixed 4x100m Medley Relay Final – Budapest, Hungary – July 26, 2017 – Matt Grevers, Caeleb Remel Dressel and Lilly King of the U.S. team celebrate after winning the race and breaking the World Record. REUTERS/Michael Dalder TPX IMAGES OF THE DAY 

Swimming – 17th FINA World Aquatics Championships – Mixed 4x100m Medley Relay Final – Budapest, Hungary – July 26, 2017 – Matt Grevers, Caeleb Remel Dressel and Lilly King of the U.S. team celebrate after winning the race and breaking the World Record. REUTERS/Michael Dalder 

Swimming – 17th FINA World Aquatics Championships – Mixed 4x100m Medley Relay Final – Budapest, Hungary – July 26, 2017 – Matt Grevers, Caeleb Remel Dressel and Lilly King of the U.S. team celebrate after winning the race and breaking the World Record. REUTERS/Michael Dalder 

Swimming – 17th FINA World Aquatics Championships – Men's 100m Backstroke awarding ceremony – Budapest, Hungary – July 25, 2017 – Matt Grevers (silver) of the U.S. poses with the medal. REUTERS/Michael Dalder 

Swimming – 17th FINA World Aquatics Championships – Men's 100m Backstroke awarding ceremony – Budapest, Hungary – July 25, 2017 – (L-R) Matt Grevers (silver) of the U.S, Jiayu Xu (gold) of China and Ryan Murphy (bronze) of the U.S. pose with the medals. REUTERS/Michael Dalder 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Swimmer Matt Grevers poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 7, 2016. "I like listening to Monsters of Men, Incubus," said Grevers. "I think about what it felt like in 2012 to stand on top of the podium and I think I want it again." REUTERS/Lucy Nicholson SEARCH "THE WIDER IMAGE" FOR ALL STORIES. 

Matt Grevers of the U.S. celebrates with his silver medal after winning the men's 50m backstroke final at the Aquatics World Championships in Kazan, Russia, August 9, 2015. REUTERS/Stefan Wermuth

Camille Lacourt of France is congratulated by second placed Matt Grevers of the U.S. (L) after winning the men's 50m backstroke final at the Aquatics World Championships in Kazan, Russia, August 9, 2015. REUTERS/Michael Dalder

Third placed Matt Grevers of the U.S. poses with his bronze medal after the men's 100m backstroke final at the Aquatics World Championships in Kazan, Russia, August 4, 2015. REUTERS/Hannibal Hanschke

France's second placed Camille Lacourt, Australia's first placed Mitchell Larkin and third placed Matt Grevers of the U.S. (L-R) pose with medals after the men's 100m backstroke final at the Aquatics World Championships in Kazan, Russia, August 4, 2015. REUTERS/Michael Dalder

Camille Lacourt of France, Mitchell Larkin of Australia and Matt Grevers from the U.S. (L-R) react after the men's 100m backstroke final at the Aquatics World Championships in Kazan, Russia August 4, 2015. REUTERS/Michael Dalder

Matt Grevers of the U.S. reacts after the men's 100m backstroke semi-finals at the Aquatics World Championships in Kazan, Russia, August 3, 2015. REUTERS/Michael Dalder 

Matt Grevers of the U.S. starts in the men's 100m backstroke semi-finals at the Aquatics World Championships in Kazan, Russia, August 3, 2015. REUTERS/Hannibal Hanschke

Matt Grevers of the U.S. starts in the men's 100m backstroke semi-finals at the Aquatics World Championships in Kazan, Russia, August 3, 2015. REUTERS/Hannibal Hanschke

Matt Grevers of the U.S. swims in a men's 100m backstroke heat during the Aquatics World Championships in Kazan, Russia August 3, 2015. REUTERS/Hannibal Hanschke

Matt Grevers of the U.S. swims in a men's 100m backstroke heat during the Aquatics World Championships in Kazan, Russia August 3, 2015. REUTERS/Hannibal Hanschke TPX IMAGES OF THE DAY

Matt Grevers of the U.S. swims in a men's 100m backstroke heat during the Aquatics World Championships in Kazan, Russia August 3, 2015. REUTERS/Hannibal Hanschke

Matt Grevers of the U.S. prepares to start in a men's 100m backstroke heat during the Aquatics World Championships in Kazan, Russia August 3, 2015. REUTERS/Hannibal Hanschke

Matt Grevers from the U.S. reacts after the men's 100m backstroke heats at the Aquatics World Championships in Kazan, Russia August 3, 2015. REUTERS/Michael Dalder

Matt Grevers from the U.S. prepares before the men's 100m backstroke heats at the Aquatics World Championships in Kazan, Russia August 3, 2015. REUTERS/Michael Dalder

Silver medalist Matt Grevers of the U.S. poses with his medal at the men's 50m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona August 4, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Gold medallist Camille Lacourt (C) of France poses with other medallists at the men's 50m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona August 4, 2013. France's Jeremy Stravius (R) finished second and took the silver medal, while Matt Grevers of the U.S. finished third and took the bronze. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Silver medalist Matt Grevers of the U.S. poses with his medal at the men's 50m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona August 4, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Gold medalist France's Camille Lacourt (C) poses with silver medalists compatriot Jeremy Stravius (R) and Matt Grevers of the U,S, at the men's 50m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona August 4, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers (C) of the U.S., David Plummer of the U.S. and France's Jeremy Stravius start the men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Gold medallist Matt Grevers (C) of the U.S. poses with other medallists at the men's 100m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. David Plummer of the U.S. (L) finished second in the event and took the silver medal, while France's Jeremy Stravius finished third and took the bronze. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. poses with his gold medal at the men's 100m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Gold medalist Matt Grevers of the U.S. poses with his medal at the men's 100m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Gold medalist Matt Grevers of the U.S. (C) poses between silver medalist David Plummer of the U.S. (L) and bronze medalist France's Jeremy Stravius at the men's 100m backstroke victory ceremony during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. (R) is congratulated by second place and compatriot David Plummer after winning the men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. blows a kiss after winning the men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. swims in the men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING TPX IMAGES OF THE DAY)

Matt Grevers of the U.S. starts his men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. reacts after winning the men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. reacts after winning the men's 100m backstroke final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. checks his time after swimming in the men's 100m backstroke semi-final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 29, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Matt Grevers of the U.S. competes in the men's 100m backstroke heats during the World Swimming Championships at the Sant Jordi arena in Barcelona July 29, 2013. REUTERS/Albert Gea (SPAIN - Tags: SPORT SWIMMING)

Michael Phelps of the U.S. celebrates with his gold medal after winning the men's 4x100m medley relay final during the London 2012 Olympic Games at the Aquatics Centre August 4, 2012. Phelps ended his incredible Olympic career on the perfect note on Saturday, winning his 18th gold medal for the United States in the men's medley relay, the last time he will swim a competitive race. Swimming the butterfly leg, the most decorated Olympian of all time went out as the ultimate winner when he joined forces with Matt Grevers, Brendan Hansen and Nathan Adrian to crush their opponents and win the gold. REUTERS/Jorge Silva (BRITAIN - Tags: SPORT SWIMMING OLYMPICS)

Michael Phelps of the U.S. poses with his gold medal after winning the men's 4x100m medley relay final during the London 2012 Olympic Games at the Aquatics Centre August 4, 2012. Phelps ended his incredible Olympic career on the perfect note on Saturday, winning his 18th gold medal for the United States in the men's medley relay, the last time he will swim a competitive race. Swimming the butterfly leg, the most decorated Olympian of all time went out as the ultimate winner when he joined forces with Matt Grevers, Brendan Hansen and Nathan Adrian to crush their opponents and win the gold. REUTERS/Jorge Silva (BRITAIN - Tags: SPORT SWIMMING OLYMPICS TPX IMAGES OF THE DAY)

Michael Phelps of the U.S. throws his winner's flower bouquet to his mother Debbie (not pictured), after receiving his gold medal for winning the men's 4x100m medley relay final during the London 2012 Olympic Games at the Aquatics Centre August 4, 2012. Phelps ended his incredible Olympic career on the perfect note on Saturday, winning his 18th gold medal for the United States in the men's medley relay, the last time he will swim a competitive race. Swimming the butterfly leg, the most decorated Olympian of all time went out as the ultimate winner when he joined forces with Matt Grevers, Brendan Hansen and Nathan Adrian to crush their opponents and win the gold. REUTERS/Jorge Silva (BRITAIN - Tags: SPORT SWIMMING OLYMPICS HEADSHOT TPX IMAGES OF THE DAY)

Michael Phelps of the U.S. poses with his gold medal after winning the men's 4x100m medley relay final during the London 2012 Olympic Games at the Aquatics Centre August 4, 2012. Phelps ended his incredible Olympic career on the perfect note on Saturday, winning his 18th gold medal for the United States in the men's medley relay, the last time he will swim a competitive race. Swimming the butterfly leg, the most decorated Olympian of all time went out as the ultimate winner when he joined forces with Matt Grevers, Brendan Hansen and Nathan Adrian to crush their opponents and win the gold. REUTERS/Jorge Silva (BRITAIN - Tags: SPORT SWIMMING OLYMPICS HEADSHOT TPX IMAGES OF THE DAY)

Matt Grevers of the U.S. swims on his way to win the men's 100m backstroke final at the London 2012 Olympic Games at the Aquatics Centre July 30, 2012. Grevers set a Olympic record with a time of 52.16 seconds. REUTERS/Jorge Silva (BRITAIN - Tags: SPORT SWIMMING OLYMPICS)

Matt Grevers of the U.S., who won gold, leads ahead of France's Camille Lacourt (C) and Japan's Ryosuke Irie (R) during the men's 100m backstroke final at the London 2012 Olympic Games at the Aquatics Centre July 30, 2012. REUTERS/Andrew Winning (BRITAIN - Tags: SPORT OLYMPICS SPORT SWIMMING)