Complex sentence: Hilbert's son Franz suffered throughout his life from an undiagnosed mental illness: his inferior intellect was a terrible disappointment to his father and this misfortune was a matter of distress to the mathematicians and students at Göttingen.
Split into simpler sentences: Hilbert's son Franz suffered throughout his life from an undiagnosed mental illness. His inferior intellect was a terrible disappointment to his father and this misfortune was a matter of distress to the mathematicians and students at Göttingen.