Frances Brandon was born on 16 July 1517 in Hatfield, Hertfordshire, and spent her childhood in the care of her mother. Although her father, the Duke of Suffolk, had obtained a declaration of nullity regarding his earlier marriage to Margaret Neville (the widow of John Mortimer) on the ground of consanguinity, in 1528 he secured a bull from Pope Clement VII assuring the legitimacy of his marriage with Mary Tudor, and therefore the legitimacy of his daughter Frances. Frances was close to her aunt Catherine of Aragon, first wife of her uncle King Henry VIII, and was a childhood friend of her first cousin, the future Queen Mary I.