The father says he did not raise his son as a Muslim — and he regrets his decision now.

Maybe if Reda Nidalha, born and bred in the historic Dutch university city of Leiden, had learned about moderate Islam, it would have been harder for extremists to "brainwash" him and help him travel to Syria, his father says.

Mohamed Nidalha sent his son to Belgium to stay with his uncle after Reda fell in with a bad set of friends in Leiden.

But Reda soon came into online contact with a Belgian in Syria who linked him up with a notorious terror recruiting network, Sharia4Belgium.

The 20-year-old who grew up liking girls and going to discos suddenly changed, thanks to a toxic cocktail of online propaganda and covert contact with extremists in Belgium, one of Europe's hotspots for Islamic radicals.

"He went to the mosque, grew a beard and went to readings somewhere in a secret place — not in a mosque, but in a house somewhere," says Nidalha, a 49-year-old immigrant from Morocco who works in a concrete factory. "There, he was brainwashed, and prepared. Inside two months he was made totally crazy."

Reda is emblematic for hundreds of disaffected Muslim youngsters from the largely secular countries of Belgium and the Netherlands who have turned their backs on their liberal Western societies and been sucked into the sectarian maelstrom of Syria's brutal civil war.

"It is 100 percent that he is with ISIS. It's something everybody can see — he is on Facebook, he doesn't cover his face," Nidalha says, referring to the Islamic State militant group. "I've asked him: 'Reda, why do you do that?' and he says, 'Papa, you don't have to worry about me. That is my life. I want to live it that way.'"

Nidalha is at a loss to explain why exactly his son turned to violent extremism while trying to make a fresh start in Belgium.

But he suspects the jihadi recruiters saw in his son an easy mark — a kid from a broken home struggling with life and looking for a new direction.

"Those people are professional," Nidalha said. "They pick on the easiest prey they can easily brainwash."

He is angry at the Dutch government for not doing more to prevent his son from reaching Syria, saying they could have issued an international arrest warrant for him while he was in Turkey waiting to cross the border. Mohamed says his son told him he was detained twice by Turkish authorities before he got to Syria.

A Dutch intelligence agency estimates that around 180 Dutch citizens left the country to fight in 2014 alone.

Reda has been gone for almost a year now. His mother, Nidalha's ex-wife, still can't come to terms with what feels increasingly like an irreversible loss.

Nidalha is certain he won't see his boy alive again, but worries what he would be like if he did manage to return home.

"Imagine my son comes back. What kind of son do I get back? I don't get the same son as before," he said. "Because my son has now learned things there in Syria. My son might be able to make bombs now, maybe he can shoot."