(CNN) -- As a teenager, Jejoen Bontinck danced in music videos and was a regular kid hanging out with friends in Antwerp, Belgium. But within a year, he went from a hip-hop-loving teenager to a young Muslim convert, preaching on the streets of Antwerp.
His father, Dimitri Bontinck, claims that in 2010, when Jejoen was 15, he became infatuated with a Moroccan girl, which eventually led to him converting to Islam.
His parents started noticing a radical change in their son about eight to nine months after the conversion.
"He started to become very religious. He stopped wearing his normal clothes. So we really see the progress of radicalization -- this is the right word -- we really see the signs," Dimitri explained.
Dimitri says he called the authorities after his son joined a radical Muslim organization in Belgium, but they took no action. "[They told me] there is no law forbidding a child to be a member of this organization," Dimitri says. "It's freedom of speech. Its freedom of religion. Its freedom of organization."
When Jejoen, still a teenager, asked his parents if he could move to Cairo to study Islam last year, they said yes. But Dimitri knew something was wrong when Jejoen didn't call his sister on her birthday -- and he began to believe that his son wasn't in Egypt at all.
Dimitri searched for clues online to where his son really was, and he was shocked by what he found -- videos and pictures of his son's hometown friends in Syria.
"It was Syria this, Syria that. One day I find a video ... of friends of his from Antwerp. So when I saw that, I knew right away -- my son is there," he says.
So Dimitri, a former Belgian soldier who says he used to work with the U.N., decided to go after Jejoen himself. He took out an ad in a local newspaper asking for volunteers to take him to Syria.
In April of last year, a Dutch war reporter agreed to accompany Dimitri to Syria, but their trip turned up few leads on where Jejoen might be. So six months later, Dimitri returned to the war-torn country on his own.
Dimitri says it didn't take long before he encountered some of the militants who were fighting to bring down the regime of Syrian President Bashar al-Assad. Dimitri says he was warned that he would be killed by the Islamists, but instead they took him in.
Along the way, Dmitri shot videos of his time in Syria. In one he appears to sympathize with the militants, even parading around with their weapons. "They took me in and they all respect me," he says. "I was eating with leaders (of these groups) and they pray for me."
"I have been in Syria and I meet with so many groups like Jabhat al-Nusra ... and I am not Muslim. And when you see what these people have done for me! They arranged for my sleeping and food."
Jabhat al-Nusra, a hard-line al Qaeda affiliate, is one of the most notorious groups operating in Syria today. Dimitri says militants from the group nearly beat him to death.
"They beat me, they almost killed me," he says. "They took all my clothes off. They put a cap on me, they put cuffs on me. And I was almost dead, because always they suspect [I was] CIA," he says.
But in the end, Dimitri says, they let him go -- and led him to his son, who he says was living with al-Nusra militants at the time.
Dimitri gets emotional when describing what it was like to come face to face with his son for the first time inside Syria.
"I never cried before when I was searching for him, when I didn't know anything," he says. "But the first physical contact -- I held him like a small baby. I was really in harmony with him. And he was too. Because he was like a children who has lost his way."
But the saga didn't end when Dimitri and his son boarded the plane home. Police detained Jejoen, now 19, when they landed in Belgium, and charged him with participating in a terrorist organization. Jejoen says he was only there to deliver medical supplies to the group.
Jejoen is now at home with his dad, but he is being closely monitored by Belgian authorities as he awaits his trial, which is expected to begin at the end of June. He is barred from speaking to the press.
Dimitri insists his son is innocent and says that the Belgian authorities haven't done enough to keep their own citizens safe from extremist groups.
Many questions remain unanswered. What was Jejoen's role inside Syria? Was he truly on a humanitarian mission?
There are more questions than answers as Jejoen's day in court approaches -- but for both father and son, the journey has transformed their lives forever.