The Honourable Antonia Georgiana Isabella St. John was the daughter of Henry Joseph St John and his wife Lady Isabella Frances née Fitzroy, a daughter of the 4th Duke of Grafton. According to the IGI, she was christened at St. Nicholas’s Church in Brighton on 26 December 1832.

At the time of the 1851 census, Antonia was 18 and living with her parents at 8 Eccleston Street in London. She gave ‘Brighton’ as her place of birth. Also present on the night of the census were five servants.

She appears on the 1861 census, aged 28, living with her mother, Lady Isabella St. John, at Hampton Court Palace. Her mother was by now a widow, her father having died on 2 January 1857. Also present on the night of the census were four servants, including a footman.

Hon Antonia St John never married. She died in 1903, aged 71. The death was registered in the district of Potterspury in Northamptonshire.