Humanitarian Moira Kelly texted her adopted son Ahmed before his Paralympic final to tell him she was right behind him.

He didn't need reminding.

Born with significant disabilities in all four limbs, he knows he and his brother Emmanuel hit the jackpot the day she took them from a Baghdad orphanage to Australia for medical treatment in 1998.

Moira and Emmanuel were in the stands at the Olympic aquatic centre on Monday night for Ahmed's SB3 50m breaststroke.

Ahmed finished fourth, two seconds off bronze in the SB3 50m breaststroke.

"It was not quite the ending that I was after," he said.

"I just wanted to go out there and race, I was so nervous.

"First final of the Paralympic Games, getting your name called and walking up to your blocks.

"It was just unreal."

He said he had been touched by the warm response to his story from the Australian public and thanked his mother.

"She was fantastic just to get me out here to give me this brand new opportunity," he said.

"Australia has embraced me and I can't thank you enough."

The ambitious 20-year-old has set his sights on the Rio Games in 2016.

"This is just the taste of what is possible," he said.

"Come Rio, bring it on. I am going to work my butt off to get on the podium in Rio."