Former private schoolboy John Zakhariev, 21, (pictured) has been reportedly arrested in Bulgaria on terrorism charges

A former private schoolboy who allegedly tried to join Islamic State in the Middle East in 2013 has reportedly been arrested in Bulgaria on terror charges.

John Zakhariev, 21, allegedly travelled to Syria for a short time after he graduated from Sydney's catholic school for boys Waverley College in 2012, Fairfax Media reported.

But Bulgarian authorities allege the Sydney man - who is the son of a Vietnamese mother and a Bulgarian father - was sent packing in 2013 because he was not competent for combat training.

Authorities allege Zakhariev had travelled to Bulgaria last year to train himself at shooting ranges after he obtained a Bulgarian passport.

Mr Zakhariev admits visiting a legal shooting range in Bulgaria, but denies it was for 'training' purposes.

However, he claimed he only wanted the passport so he could travel in the EU and to help his father, 82, a former UN diplomat, move back to his homeland to retire.

Mr Zakhariev's lawyer Hristo Botev told the publication the allegations he was preparing himself for the terrorist group were 'absurd'.

The man allegedly travelled to Syria after graduating from Sydney's Waverley College in 2012

His 25-year-old sister Nevena Zakhariev told Fairfax Media the family thought it was a joke when her brother was arrested.

'At first, I just thought it was a big misunderstanding, we laughed it off thinking he'd be home in a couple of weeks because he's done nothing wrong,' she said.

'But as months and months passed, it became more serious. My fear is that the government wants to make an example out of him and he'll go to jail for something he didn't do.'

The man has been detained since September last year as he's expected to front a court hearing on March 17.

'The Department of Foreign Affairs and Trade is providing appropriate consular assistance to an Australian man detained in Bulgaria, in accordance to the Consular Services Charter,' a DFAT spokesperson told Daily Mail Australia.