Lady Jane Grey - Wikipedia

On July 10, 1553, Lady Jane Grey, daughter of the Duke of Suffolk, was proclaimed Queen of England, succeeds Edward VI, who proclaimed his half-sisters illegitimate. She reigned for nine days. From the article:

"Lady Jane Grey (c. 1537[3] – 12 February 1554), known also as Lady Jane Dudley (after her marriage[4]) and as "the Nine Days' Queen",[5] was an English noblewoman and de facto Queen of England and Ireland from 10 July until 19 July 1553.

Jane was the great-granddaughter of Henry VII through his younger daughter Mary, and was a first cousin once removed of Edward VI. She had an excellent humanist education and a reputation as one of the most learned young women of her day.[6] In May 1553, she married Lord Guildford Dudley, a younger son of Edward's chief minister John Dudley, Duke of Northumberland. In June 1553, Edward VI wrote his will, nominating Jane and her male heirs as successors to the Crown, in part because his half-sister Mary was Roman Catholic, while Jane was a committed Protestant and would support the reformed Church of England, whose foundation Edward claimed to have laid. The will named his half-sisters Mary and Elizabeth illegitimate and removed them from the succession, subverting their claims under the Third Succession Act.

After Edward's death, Jane was proclaimed queen on 10 July 1553 and awaited coronation in the Tower of London. Support for Mary grew very quickly, and most of Jane's supporters abandoned her. The Privy Council of England suddenly changed sides and proclaimed Mary as queen on 19 July 1553, deposing Jane. Her primary supporter, the Duke of Northumberland, was accused of treason and executed less than a month later. Jane was held as a prisoner at the Tower and was convicted of high treason in November 1553, which carried a sentence of death—though Mary initially spared her life. However, Jane's father, Henry Grey, 1st Duke of Suffolk, became part of Wyatt's rebellion against Queen Mary's intention to marry Philip II of Spain, and Jane was viewed as a threat to the Crown. Both she and her husband were executed on 12 February 1554."