ASHLEY Callus said his best swims were ahead of him in the lead up to the Olympic Games, and he proved that on Saturday when he narrowly missed out on a medal in the 50m freestyle.

The 29-year-old swam a personal best time of 21.62 seconds to finish fourth in the sprint, 0.13 seconds behind bronze medallist Alain Bernard, of France.

Brazilian Cesar Cielo Filho won the gold in a time of 21.30 and Frenchman Amaury Leveaux took silver in 21.45. World record-holder Eamon Sullivan finished sixth.

Ashley's fourth place in what has been billed by many as the "fastest race ever" caps off a remarkable comeback after a lacklustre performance at the Athens Olympics.

The Redlander - who had previously won Olympic gold in the 4x100m relay in Sydney - crashed out in the 50m heats and took a year off swimming.

After a stint at the Gold Coast, Ashley returned to Cleveland last November to mount his Olympic campaign under the guidance of coach Chris Urquhart.

His performance in Beijing, which included a bronze in the 4x100m earlier last week as well as the fourth, will no doubt make up for the disappointment four years ago.

Ashley told Channel 7 after the race that he was happy with what he'd accomplished in Beijing.

"I'm absolutely rapt," he said.

"Over the years there's been a lot of blood, sweat and tears."

Speaking from Beijing, his former coach David Urquhart - now president of Swimming Australia - told the Bayside Bulletin Ashley would have liked the bronze, but was very pleased with his result.

"He said to me he's the happiest fourth place-getter at any Olympics," David said.

"He did the best he could and he couldn't have swum any better."

David hosed down speculation that Ashley might abandon his decision to retire after the Olympics.

"That was always the plan, he wasn't intending to swim on after Beijing," David said.

"He could change his mind after three months off, but I don't think he will.

"I spoke to him last night and I think he's just happy with the way it ended."