Doting father: Josef Stalin, pictured with his daughter Svetlana Alliluyeva, disowned his son Yakov in 1928 A Soviet archive has yielded up one of the last secrets of World War Two that dictator Josef Stalin took to his grave – the fact his son Yakov gave himself up to Nazi forces during the 1941 invasion of his country. The party line in Stalin’s Russia was always that Yakov Dzhugashvili,...