Both Margaret and Mary were daughters of Sir John Shelton and his wife Anne, the sister of Thomas Boleyn, 1st Earl of Wiltshire, the father of King Henry VIII's second Queen consort, Anne Boleyn. Margaret and Mary were thus first cousins of the Queen. Margaret was the youngest of Sir John Shelton's daughters. She was an attendant of her cousin, Queen Anne Boleyn, and was present when she made her first appearance as queen on Easter Eve, 12 April 1533.
One of the Shelton sisters is believed to have been King Henry's mistress for a six-month period beginning in February 1535, according to statements about mistresses made by the Imperial ambassador, Eustace Chapuys, who referred to Mistress Shelton.
According to biographer Antonia Fraser, this was Margaret Shelton. Chapuys was always at court when in England, more frequently so than most contemporaneous writers. Hugh Latimer identified Madge Shelton as the woman attendant on Anne when she miscarried within hours of Queen Katherine of Aragon's death. Madge was the "concubine's" closest companion in waiting owing to her familial ties, yet would be dismissed at the end.
However, more recent research has suggested that it was Margaret's sister Mary who was Henry's mistress, and was rumoured to have been selected to become his fourth wife. Supposedly, the confusion of earlier historians arose from the label "Marg Shelton", in which the "y" resembled a "g", a common confusion in sixteenth-century writing.
Once arrested, Anne Boleyn was attended by four unsympathetic ladies, who had been instructed by the King's chief minister Thomas Cromwell to report on the Queen's actions. Anne told one of these ladies, Mrs. Coffin, that she had reprimanded Francis Weston for flirting with Madge Shelton, who was betrothed to Henry Norris. Anne wondered aloud to Weston why Norris had not married Shelton yet. Weston replied, "[Norris] came more to her [Anne's] chamber for her than for Madge." Both Norris, Madge Shelton's betrothed, and her supposed lover Weston, were executed on charge of having been Anne Boleyn's lovers.
Margaret Shelton is the narrator in Jean Bruller (Vercors)' 1985 book Anne Boleyn (originally written in French), in which Anne Boleyn is presented as a far-sighted English patriot, who strove to make England strong and independent by ending its dependence on the Catholic Church and building up its navy. As depicted in the book, Margaret Shelton was Anne Boleyn's closest and most loyal companion throughout her life, shared her vision for England, and lived to impart it to her daughter, the future Queen Elizabeth I.
- Richardson 2004, p. 179; Weir 1991, p. 277.
- Weir, Henry VIII, p.335
- Kelly Hart, The Mistresses of Henry VIII, The History Press, 2009
- CSP Spanish, V, pt.2, p.126
- Weir 1991, p. 277.
- Antonia Fraser The Six Wives of Henry VIII
- Spanish Calendar of Letters, Despatches and State Papers relating to Negotiations between England and Spain; Weir, p.15
- Ives 2005, pp. 334–335.
- Richardson, Douglas (2004). Plantagenet Ancestry: A Study in Colonial and Medieval Families, ed. Kimball G. Everingham. Baltimore, Maryland: Genealogical Publishing Company Inc. Retrieved 17 March 2011.
- Weir, Alison (1991). The Six Wives of Henry VIII. New York: Grove Weidenfeld.
- Weir, Alison (2001). Henry VIII: King and Court. London. ISBN 0-224-06022-8.
- Weir, Alison (2009). The Lady in the Tower: The Fall of Anne Boleyn. London. ISBN 978-0-224-06319-7.
- Herman, Peter C., ed. (1994). Rethinking the Henrician Era: Essays on Early Tudor Texts and Contexts. University of Illinois Press. pp. 40–77.
- Hart, Kelly (2009). The Mistresses of Henry VIII. Stroud, Gloucestershire: The History Press. pp. 120–128. ISBN 978 0 7524 4835 0.