The other candidate is Sir John Champernowne, whose wife was approximately 43 at the time of Kat's birth, which some people believe to be too old, but Catherine Knollys had her last child at 38. Sir John died a year after her birth, but the fact that Kat wrote to Cromwell in 1536 mentioning her father in the present tense suggests he isn't her father, unless an unknown stepfather is meant. If Kat "was" the child of Sir John Champernowne, then her niece was Joan Champernowne, who married Sir Anthony Denny, Groom of the Stool and most trusted servant to King Henry VIII.