The Jewish population of Linz was expelled in July 1938. Kronberger's mother was killed at Schloss Hartheim and his sister was gassed at Auschwitz. His father survived imprisonment in the concentration camp at Theresienstadt. Kronberger became a naturalised British citizen in 1946. In 1951 he married Joan Hanson, a scientific assistant at Harwell, a widow with a young son, Paul; together they had two daughters, Zoë and Sarah. Joan was diagnosed with a brain tumour in 1952 and died in 1962. Kronberger was a talented pianist, and also a skilled mountaineer and skier.