An American who left his hometown to fight for the Islamic State in Iraq and Syria (ISIS) died in a battle against a rival terror group in Syria.

Douglas McAuthur McCain, 33, was identified by authorities. He left San Diego last year to fight for the group, and was killed in northern Syria near the Turkish border, reported the New York Times.

According to CNN, McCain was killed in a battle with the al-Nursa Front. They are an organization that has been linked to al-Qaeda and has been labeled a foreign terror group by the U.S. government.

Ken McCain, the uncle of Douglass, said the family was shocked when his nephew went to fight for ISIS. He described him as “a good person, loved his family, loved his mother, loved his faith.” Douglass practiced Christianity before converting.

Ken McCain said that Douglass converted to Islam several years ago. Family members became alarmed when they saw Douglas McCain's Facebook posts in which he sympathized with ISIS, and when he traveled to Turkey. Before he died, U.S. investigators were looking into his activities.

McCain is just one of the many American who have traveled to Syria to fight. At least 100 other Americans have traveled, and a few are suspected to have died while fighting.