They never said he'd go head-to-head with the real thing, but when viewers tuned in to watch Michael Phelps race a great white shark, many were disappointed.
That's because the 23-time Olympic gold medalist didn't race a shark at all, but a computer-generated simulation.
And he didn't even win.
Turns out “Michael Phelps races a shark” was really just “Michael Phelps swims alone and then compares his time to a shark’s time.”— Gary Parrish (@GaryParrishCBS) July 24, 2017
Phelps lost the race — part of the Discovery Channel's Shark Week special Phelps vs. Shark: Great Gold vs. Great White — to the simulated shark by two seconds.
Folks who tuned in to the special saw the Great White in one lane and Phelps right next to it while wearing a special fin to mimic a shark's tail.
But in reality, they were never in the water together. Instead, it was a CGI shark animated into footage of Phelps swimming in the waters off South Africa.
I know it's stupid to think michael phelps was actually going to be racing against a real shark but I'm stupid and upset— Nicole (@nicoleee_adams) July 24, 2017
Despite clues Phelps gave in interviews leading up to the "race," many viewers didn't seem to understand that the Olympian would never actually come fin-to-fin with the man-eater.
"Turns out “Michael Phelps races a shark” was really just 'Michael Phelps swims alone and then compares his time to a shark’s time,'" Gary Parris, a sports analyst for CBS Radio tweeted, part of a chorus of posts about the so-called "race."
Another Twitter user wrote: "i spent 60 minutes of my life watching a build up to Michael Phelps race a fake computer generated shark..."
While admitting it was probably a long shot, another viewer expressed her extreme disappointment.
"I know it's stupid to think Michael Phelps was actually going to be racing against a real shark but I'm stupid and upset," tweeted @nicoleee_adams.
When he took to Twitter himself after the show aired, Phelps declined to address any of the unmet expectations.
"Rematch? Next time..warmer water," Phelps wrote.
Judging from the backlash, that rematch seems unlikely.