Macmillan was the son in law of Spencer Cavendish 8th Duke of Devonshire, having married the 8th Duke’s daughter Dorothy. Elizabeth Christiana Hervey Duchess of Devonshire, the second wife of William Cavendish 5th Duke of Devonshire, was reputed to be the mother of Frederick Hervey Foster Quin, the founder of the London Homeopathic Hospital,
Dorothy Macmillan’s great uncle was Spencer Cavendish 8th Duke of Devonshire, the leader of the Liberal Party in the 1870s, and a close colleague of William Ewert Gladstone (who was a patient of homeopath James Manby Gully and Joseph Kidd), Joseph Chamberlain (the father of Arthur Neville Chamberlain, who worked with homeopath, journalist and historian J Ellis Barker). Spencer Cavendish 8th Duke of Devonshire was the driving force behind the foundation of the University of Birmingham and was its first Chancellor, alongside homeopath James Gibbs Blake, President, Chairman of the Trustee and the Chairman of the Council of the Mason Science College in Birmingham, and a Co Founder and Vice President of the University of Birmingham, and Josiah Mason, a Trustee and member of the Management Committee, and major sponsor of the Birmingham Homeopathic Hospital and the Co-founder of the Mason Science College in Birmingham, which evolved into the University of Birmingham.
Lady Dorothy Macmillan had a long affair with the Conservative politician Robert Boothby, in full public view of Westminster and established society. Robert Boothby was widely rumoured to have been the father of Macmillan’s youngest daughter Sarah.
Sarah Macmillan was raised by the Macmillan’s as their own daughter – an echo of the reputed birth of Frederick Hervey Foster Quin to Elizabeth Christiana Hervey Duchess of Devonshire, though in 1799, Frederick Hervey Foster Quin was quietly fostered out of sight. Nevertheless, Frederick Hervey Foster Quin became the personal physician to the Elizabeth Duchess of Devonshire, attending her in her final illness in 1824.
Whether this trait is typical of English aristocracy, or a trait of the family of the Dukes of Devonshire, the parallels are there nontheless.