Los Angeles - Michael Phelps, the greatest Olympian of modern times, has finally met his match in a swim-off against the greatest predator in the oceans, the great white shark.
But many viewers of the Discovery Channel's much-publicised race between man and beast found the result to be a little fishy.
Touted as "Phelps vs. Shark: Great Gold vs. Great White," the face-off in the chilly, shark-rich waters off South Africa was the launchpad for the channel's annual Shark Week series of shows.
Phelps, who has won 28 Olympic medals including 23 golds, noted before the event that his safety was the number one priority going into the race, and said before the broadcast that he did not actually enter the water with the shark he was racing.
Instead, the film crew shot footage of a shark speeding along the same stretch of water as Phelps, who swam the course at a different time under the supervision of marine experts and divers.
The filmmakers used special effects to splice the two together, so it looked as though the American swimmer was racing alongside the huge predator.
Despite being fitted with a special monofin to help propel him through the water, Phelps lost by two seconds to the shark, which put on a final spurt as it closed in on a seal.
After his narrow defeat, Phelps demanded a rematch. "Next time... warmer water," the 32-year-old champion wrote on Twitter.
Many viewers of the show also took to social media to express their disappointment, having apparently believed Phelps would actually be racing a shark in real time.
"Call me crazy but I thought they were gonna put Phelps up against a real shark not a simulation. I feel robbed," said a Twitter user who goes by Meg Conley.
Another scornful Twitter user posted footage of a cartoon shark dancing with the caption "Live footage of Shark getting ready to wipe the floor with Michael Phelps."
Others, however, expressed surprise that anyone would have believed a real one-on-one between man and shark would have been possible.