Douglas's only child, Raymond, was diagnosed with schizoaffective disorder in 1927, at the age of 24 and entered St Andrew's Hospital, a mental institution. He was decertified and discharged after five years but suffered another breakdown and returned to the hospital. In February 1944, when his mother died of a cerebral haemorrhage at the age of 70, Raymond was able to attend her funeral and in June he was again decertified. His conduct rapidly deteriorated and he returned to St Andrew's in November. He stayed there until his death on 10 October 1964. He never married.