Lady Jane Grey, (1536/7 — 12 February 1554), a great-granddaughter of Henry VII of England, reigned as uncrowned Queen Regnant of the Kingdom of England for nine days in July 1553, and for that reason is called "The Nine Days Queen". blank">Official Website of the British Monarchy – Jane

Some authorities claim that Jane's accession, pursuant to the will of _Edward VI, breached the laws of England as it is suggested Mary Tudor was the legitimate and rightful heir to the Crown. Mary had, however, been declared illegitimate by her father, Henry VIII. The same ruling had been applied to her younger half-sister, Elizabeth, later Elizabeth I. Many high-ranking nobles proved themselves pliable to accepting Jane as Queen of England. Acting largely out of financial self-interest, they supported her even if only as part of a power struggle to stop Henry's first-born child, Princess Mary, a Roman Catholic, from ascending to the throne. The rule of Jane, a Protestant, soon ended when the authorities abandoned their support for her as Queen when they realised Mary had won the day. Mary subsequently had Jane executed for treason, following another attempt to seize the crown for Jane by her supporters.

Popular history sometimes refers to Lady Jane as "The Nine Days' Queen" (10 July — 19 July 1553) or, less commonly, as "The Thirteen Days' Queen" (6 July — 19 July 1553) — owing to uncertainties as to when she succeeded to the throne. Historians have taken either the day of her predecessor's death (6 July) or that of her official proclamation as Queen (10 July), as the beginning of her short reign.

Lady Jane had a reputation as one of the most learned women of her day, and the historical writer Alison Weir describes her as one of "the finest female minds of the century".