Sharky Jama, a former model from Melbourne, was shot in Syria, and previously lived in Fallujah, an Iraqi city taken over by Islamic State militants, SBS reported on Wednesday night.
Mr Jama's father, Dada Jama, had been told by someone from Syria that his son had been shot. He believed the news when he tried to call his son's phone, and was sent straight to his voicemail.
"He got a text message and he received a phone call from Syria, someone has told him his son has passed away. Then he said I tried his number, because he has contact with his son. Automatically, it goes to voicemail, that's what he said, and then he knew that his son is gone," SBS Somali radio broadcaster Ibrahim Mohamed said.
Mr Mohamed said Dada Jama would be speaking to the Somali community to urge them to ensure their children don't fall prey to militants.
Condolences have been posted on Facebook, where Jama's friends have been mourning his death.
Australian teenager Jake Bilardi, who left Melbourne last August to join Islamic State was also believed to have died, in a suicide bombing attack in Iraq in March.
Sources linked to Islamic State (IS) reported that the 18-year-old, from Craigieburn in Melbourne's northern suburbs, was involved in a suicide attack on the city of Ramadi in Iraq.
- Sidney Morning Herald with AAP