Lady Jane Grey was the great–granddaughter of King Henry VII, through his younger daughter Mary. Jane's mother – Frances Grey, Duchess of Suffolk – was Princess Mary's second child and eldest daughter. So Jane's great–grandparents were Edward's grandparents, and this makes them first cousins, once removed.
Edward, a Protestant, was keen to exclude his Catholic sister, Mary, from the succession. Shortly before his death he drafted a will, in which he restricted the succession to male descendants of Frances Grey and her daughters – of which there were none. In June 1553 he amended this will, naming "Lady Jane and her heirs male" as his successors.
This went against the wishes of Edward's father, Henry VIII, who (having previously had his two daughters, Mary and Elizabeth, declared illegitimate) had ultimately supported the rights to succession of each of his three children. Only if none of them should leave descendants would the throne pass to the heirs of his younger sister, Mary – which, as we've seen, included Jane.
In any case, Jane's mother was still alive, and the descendants of Henry VII's elder daughter, Margaret (who'd married into the Scottish royal house and nobility) had a better claim. We don't know why Edward settled on Jane, but it's hard to ignore the fact that in May 1553 (one month before Edward, on his deathbed, had amended his will) Jane had married Lord Guilford Dudley, the eldest son of John Dudley, Duke of Northumberland – Edward's chief minister.
Edward died on 6 July 1553, and Jane was proclaimed queen in the streets of London – despite the murmurings of discontent.
© Haydn Thompson 2021