King Edward fell ill in early 1553 . He drew up a document , " My Devise for the Succession " , whose final version of June 1553 was to settle the Crown on his Protestant cousin Lady Jane Grey , overturning the claims of his half @-@ sisters Mary and Elizabeth . Jane Grey was the daughter of Frances Grey , Duchess of Suffolk , a niece of Henry VIII by his younger sister Mary . On 25 May 1553 three matrimonial alliances was celebrated at Durham Place , the Dudleys ' London town mansion . Two of their younger children was concerned : Guildford , aged about 17 , married Lady Jane Grey , while Katherine , who was between eight and ten years old , was promised to the Earl of Huntingdon 's heir , Henry Hastings . A few months later these matches came to be seen as proof of a conspiracy by the Duke of Northumberland to bring his family to the throne . At the time the marriages took place , however , their dynastical implications was not considered significant by even the most suspicious of observers , the Imperial ambassador Jehan de Scheyfye . Modern historians have considered them either as part of a plot , or as " routine actions of dynastic politics " , in the words of David Loades . The initiative for the matches had probably come from the Marchioness of Northampton .