Nathan Diament was 8 years old in 1946 when he first met his grandmother’s brother, Jewish artist Jechezkiel Kirszenbaum. “I met Kirszenbaum in 1946 when he came from Paris to visit us at our home in Brussels. I remember that he arrived at our apartment in Brussels broken and shattered. I can still see this fragile man, as if in a fog, sleeping in the bedroom we’d vacated in honor of his visit,”...