Flora MacDonald Mayor was born on 20 October 1872, in London, at Kingston Hill. She was the fourth child of Grotto (1830-1927) and the Rev. Joseph Bickerstet-Mayor (1828-1916), and the youngest of the identical twins of Alexandria and Jesse Mayor.
Jesse Mayor was a gifted musician and linguist who studied Italian and German in Trieste and then taught herself Spanish, Portuguese, Danish, Dutch, Gaelic and translated Icelandic legends and Zulu grammar from Danish into English; she was already over forty when her twins were born. Joseph Mayor was a professor of classical philology, and then moral philosophy at King’s College, London. On both sides of the family were important intellectuals and clergy.