Ariarne Titmus' 400-metres freestyle win at the short course world championships on Friday sent a message to Katie Ledecky that the undisputed queen of distance swimming might have some serious competition at the 2020 Tokyo Olympics.
Titmus, known as 'Terminator' in her native Australia, swam a world record time of three minutes, 53.92 seconds to take a second title of the Hangzhou meeting after winning the 200 freestyle on Wednesday.
"I am a little bit in shock actually," Titmus said in a Swimming Australia news release. "After the 200 freestyle I thought I had a chance, but I don't really think about that type of thing, I just wanted to do my race."
The victory might have been a little hollow given that American Ledecky was not in China as she does not compete internationally in short course events.
Races in the 25-metre pool rely on slightly different tactics and techniques compared to events in regulation pools double the length.
In short course races, swimmers concentrate more on the turns and a faster speed of the stroke, while the long course events are more about endurance and settling into a rhythm.
Ledecky has dominated middle and long distances in the 50-metre pool, having won four individual Olympic gold medals, including the 200-400-800 treble at the Rio Games in 2016.
The 21-year-old turned professional earlier this year, forgoing her final two years of eligibility at Stanford University, so she could concentrate on competing solely in the 50-metre pool.
She beat Titmus in the 400 freestyle at the Pan Pacific Championships in Japan earlier this year, swimming the sixth-fastest time for the distance and dragging the Australian through to her first sub-four minute 400 in the process.
"It is exciting for me to see that," Ledecky said at the time. "I was the only one to go under four minutes in a textile suit for a few years now.
"So it is exciting for me to see how I put the standard out there and there are a lot of girls chasing that."
The swim no doubt gave the Brisbane-based Titmus some hope she might be able to challenge Ledecky and, with her world record on Friday, hinted that she might have finally realised what it might require to usurp the American in Tokyo.
"I have put in a lot of hard work since our trials five weeks ago as I wasn't happy with how I raced there," Titmus added.
"So I put in five weeks of really hard training and the turnaround that I have had in that time has been unbelievable.
"I have dropped six seconds in my 400 in five weeks, so it just goes to show that training hard works."