- Chalmers won the 100m freestyle Wednesday evening in Rio
- He's the youngest Australian to win a swimming gold since Ian Thorpe won in 2000
Chalmers, 18, is the first Aussie to win the 100m freestyle final since Mike Wenden took gold in Mexico City in 1968.
"It's unbelievable, I mean, I'm only 18," he told reporters after the race.
"Nathan [Adrian] is 10 years older than me and he's the reigning Olympic champion so being next to him was pretty daunting for me but I knew I had to stick to my guns."
It was a close race.
"It's definitely still sinking in that I've actually won," Chalmers said. "I was a bit worried that I glided for a bit too long at the finish but very happy with that."
Chalmers, the son of an Australian rules football player, is the youngest Aussie to win a gold medal in swimming since Ian Thorpe -- who took to Twitter to congratulate his countryman.
Chalmers classmates at Immanuel College hosted a viewing party for the final.
Students from the school told local reporters
that he's is a "nice, down to earth guy."
And their reaction to the result is pretty telling.