When former Dutch boxing champion Barry Groenteman used to visit his grandmother at her retirement home, he would often see an older man shadow-boxing. "He showed me his ring with the Star of David on it. And my grandmother would whisper: 'That's Ben Bril.'"

This is the story of a Jewish boxer from Amsterdam who had his life transformed by invasion, violence and anti-Semitism. A champion forced into hiding, then captured and sent to the Nazi concentration camps - after being betrayed by a former Olympic teammate.