Terry Hicks said his son David, 26, spoke to him by satellite telephone two weeks after the Sept. 11 attacks in the United States and told him he had joined the Taliban.
Hicks is the second Westerner this month to be caught with pro-Taliban forces in Afghanistan, after American John Walker, 20, another Islam convert, was captured two weeks ago.
He was handed over to the U.S. military, the Australian government said Monday.
"All I know is he was fighting for the Taliban and he said he was off to Kabul to defend Kabul...That's when I picked myself up from the floor," Hicks told the Herald Sun newspaper.
The fates of both Hicks and Walker remained unclear.
Australia's opposition leader Simon Crean said the government should seek immediate consular access to ensure Hicks is brought home instead of being handed over to U.S. authorities.
U.S. officials have yet to decide how to handle Walker, now being held at a U.S. marine base at a desert airstrip in southern Afghanistan. He could be charged with treason.
Both Hicks and Walker were raised in middle class suburbia and veered out of the mainstream as teenagers - but there the similarities end.
Walker's conversion from Catholicism to Islam at the age of 16 led him to Afghanistan. He never looked back after heading to Yemen to study Arabic, funded by his parents, and then to Pakistan for religious education, adopting the name Abdul Hamid.
Hicks, however, is better described as a rebel looking for a cause after dropping out of school at the age of 14.
He moved into the outback to work as a farmhand on cattle properties where he married an Aboriginal woman. The couple had two children - now aged nine and seven - but they broke up.
After a year in Japan working as a horse trainer, he returned to Adelaide and decided that the people of Kosovo were oppressed.
He set off for Europe in mid-1999 where, according to the Australian government, he joined the Kosovo Liberation Front. It was in Kosovo that it was believed he first encountered Islam.
After a brief stint back in Adelaide to study at an Islamic college, he converted to Islam, adopting the name Mohammed Dawood. He worked at removing the bones from chickens to support himself.
The president of the Islamic Society of South Australia, Wali Hanifi, said Hicks attended an Adelaide mosque in 1999 after returning from Kosovo.
The Australian government said Hicks moved to Pakistan in November 1999 and trained with the Lashkar-e-Taiba, one of dozens of Islamic groups fighting to wrest control of Muslim-majority Kashmir from India. He moved to Afghanistan in 2000 and trained with bin Laden's network.
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