Russian archive material published by Germany’s Der Spiegel magazine suggests that Dzhugashvili not only willingly surrendered to the Germans but that he was both anti-Semitic and highly critical of the Red Army when questioned by his captors.
http://www.independent.co.uk/news/world/europe/joseph-stalins-hated-son-surrendered-to-the-nazis-archives-reveal-8498745.html
http://www.independent.co.uk/news/world/europe/joseph-stalins-hated-son-surrendered-to-the-nazis-archives-reveal-8498745.html
