It was a much anticipated man versus animal challenge.
On Monday (July 24) at 8am Singapore time, Michael Phelps raced a potentially unbeatable opponent: a computer-simulated great white shark.
The race was aired on the Discovery Channel, as part of the channel's Shark Week special.
Even at his best, Olympic legend Phelps would have been unable to win the race - his top speed in the water is 9.7kmh, while a great white shark's is up to a whopping 41.8kmh.
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In an attempt to level the playing field, Phelps wore a mono-fin specially designed for the event.
The shark ultimately beat Phelps by 2 seconds, taking 36.1sec to swim 100m, while Phelps took 38.1sec.
While many expected Phelps and the shark to race side by side, the two raced separately, before a CGI shark was digitally added to footage of Phelps swimming.
Here is a look at five other times athletes have raced against animals, both on land and in the water.
1. Swimmer against two dolphins
Italian swimmer Filippo Magnini raced against a slightly less dangerous opponent than Phelps, competing against a pair of dolphins in 2011.
At a specially arranged event in a swimming pool in Torvaianica, Italy, Magnini had to swim one length of the pool while the dolphins had to swim two, given their advantage in speed.
Despite the arrangement, Magnini, who won gold in the 100m freestyle at the World Swimming Championships in both 2005 and 2007, still lost out to the dolphins.
2. American football player against an ostrich
National Football League (NFL) player Dennis Northcutt faced off against an ostrich named Thelma in 2009 and the results were mixed.
Filmed for a show called Sport Science, Northcutt won the first race against the bird easily, with a fence separating the two. The bird was running at only 22.5kmh.
In a second race within the ostrich's enclosure, the ostrich beat Northcutt, at a speed of 72.4kmh.
3. Rugby player against a cheetah
As part of an event sponsored by a conservation group, South African rugby player Bryan Habana raced against a cheetah in 2007.
As he was sprinting against the world's fastest land animal, Habana was given a 35m headstart. He still lost to the cheetah and not just once.
Habana asked for a rerun after losing the first race. But the cheetah still crossed the finish line before him.
Habana is considered one of the quickest players in international rugby, with his fastest 100m timing clocking in at 10.4sec.
4. Sprint athlete against a giraffe and a zebra
In 2003, sprint athlete Shawn Crawford went up against both a giraffe and a zebra in a 100m race.
While Crawford easily went past the giraffe, the zebra beat him to the finish line.
The race was filmed for the TV show Man Vs Beast, which was controversial due to its treatment of animals.
Crawford had better luck at the Olympics - he went on to win the 200m gold medal during the 2004 Summer Games.
5. Track and field athlete against racehorses
At the 1936 Berlin Olympics, track and field athlete Jesse Owens won four gold medals for the United States, making him the most successful athlete at the Games.
As a black athlete, his achievements undermined Adolf Hitler's Aryan supremacist ideals.
Despite Olympic glory, he was forced in the 1940s to run against racehorses in order to make a living and even won against them.
He made sure the starting pistol went off close to the horses, causing the animals to be startled and giving him a headstart.
SOURCES: The Washington Post, BBC News, Toronto Star, The Guardian, ESPN