Political Machinations
In 1543, Henry VIII passed the Third Succession Act. Perhaps growing clement in his old age, Henry passed the Act to restore Mary and Elizabeth to the line of succession, behind their brother, Edward. This replaced the First and Second Acts, which declared the girls to be illegitimate owing to Henry’s displeasure with the marriages that produced them. In 1547, he secured the possible inheritance of his daughters by passing the Treason Act, which defined any attempt to interrupt the line of succession detailed in the Third Succession Act as treason. Even beyond the grave, Henry continued to cause trouble.
The real danger in 1553 was the succession of Mary Tudor to the throne. What Henry surely cannot have realised was that Mary was a zealous Catholic with an axe to grind. After all, her mother, Catherine of Aragon, had been unceremoniously divorced and banished due to Henry’s desire for a new wife. Catherine had remained stoically quiet about the whole thing, and continued to practice Catholicism even after the Reformation. Mary, who was open about her religious beliefs, held an understandable grudge against those who had replaced Catholicism with a blasphemous new religion, disgraced her mother, and disinherited her.
Many Protestant nobles thus feared for their lives, quite apart from the reversion to Catholicism that Mary would doubtless insist upon. Fortunately, Edward’s death was not sudden, and so they had time to work out a strategy to keep Mary off the throne. Edward also opposed Mary’s claim to the throne, albeit primarily because he saw both of his half-sisters as illegitimate. Thus from his sickbed he drafted, and signed, a document superseding his father’s 1543 Act, which excluded Mary and Elizabeth from succeeding him. This was prepared and finessed with the help of his advisers, and named his heir.
His heir, as you have no doubt surmised, was Lady Jane Grey. It has been suggested that she was chosen under pressure from his Lord Protector, the Duke of Northumberland, since Edward initially named only male descendents of Frances and Jane Grey his successors. Wisely expecting opposition to this move, given his experience of the Catholic plot against him, Edward had over 100 councillors, peers, archbishops, bishops, and sheriffs sign the devise, and made his closest advisers swear to uphold the terms of the will. The document finalised on 21st June, and on the 6th July the king passed away.