A 20-year-old Canadian man reported to have been killed fighting for the Islamic State “genuinely seemed happy” when he was attending high school in Hamilton, Ont, two years ago, a former classmate says.

Federal officials are still trying to determine whether Mohamud Mohamed Mohamud was killed while fighting Kurdish forces in northern Syria last week.

Eric Walton-Ball, who attended Sir Allan MacNab Secondary School with Mohamud, is still trying to figure out how it could be possible.

“My initial reaction was disbelief,” Walton-Ball told CTVNews.ca. “I heard it from my mom over text and thought she had gotten the wrong name.”

Walton-Ball, who was a grade below Mohamud, describes him as being a “really nice guy” who always had a smile on his face. His friends called him “Mohamud cubed” or sometimes “Mohamud times three.”

Mohamud was involved in student politics and extracurricular clubs and would regularly drop into Walton-Ball’s English class to chat with the teacher, he remembers.

“How could this kid that I went to school with, a kid who was more involved in the community and more involved socially than I was, join a group like ISIS?”

Mohamud disappeared to Syria in July of last year, according to a Voice of America interview.

"It was shocking," Mohamud’s father said in the interview, which aired last week. "My son was a student, he suddenly changed.”

“He arranged his travel without my knowledge, and then he ended up in Syria,” the interview continues. “All of us (in the family) are very saddened. We did not expect he would do this.”

Hussein Hamdani, a friend of Mohamud’s family, said they are “devastated.” He described the former York University student as “well-integrated.”

“His family came to Canada from Somalia as refugees,” Hamdani, who also acts as the family’s lawyer, told Âéśš´ŤĂ˝. “They struggled while he was here, when he was a young boy. But he thrived, he did very well in school, he got a scholarship.”

But Hamdani said Mohamud began to change after secondary school.

"He started not associating with the Muslim community anymore, not going to mosque, and turning to the web to get his Islamic teaching."

When Mohamud went missing, the family contacted the police, but were told to wait for the then-19-year-old to turn up, Hamdani said. The family then traced Mohamud’s phone to Turkey, where they attempted to contact him.

“He finally responded and said I'm in Turkey, I'm going to cross over and join the resistance against Assad's regime," Hamdani said.

When the family asked Hamdani to help prevent their son from entering Syria and taking up arms against Syrian leader Bashar al-Assad, Hamdani said he reached out to the RCMP and CSIS.

“As much as CSIS and the RCMP and the family could wish and will – we all wished and willed that we could turn him around – at that moment it was too late in the ball game.”

In a statement, a spokesperson for the Minister of Public Safety and Emergency Preparedness couldn’t confirm what could be the first death of a Canadian in the anti-ISIS military campaign that has involved U.S. airstrikes.

“We’re aware of the reports, but, as you know, we do not comment on operational matters related to national security,” said Jean-Christophe de Le Rue. “This is a serious problem, and demands a strong response.”

With a report from CTV’s Katie Simpson