Edward VI became King of England and Ireland at the young age of nine after the death of his father, King Henry VIII, having been his only child with his third wife Jane Seymour. As King, Edward succeeded his father's power at only 14 years old under the guidance of the Duke of Northumberland. His health began declining in 1552 and it was apparent in 1553 that he was dying, leaving the succession of the throne uncertain between his half-sisters Mary and Elizabeth, though Edward manipulated the rules to try to leave the crown to Lady Jane Grey and her male heirs instead.