Lady Catherine Grey (sometimes spelled "Katherine") (August 1540 - 26 January 1568), Countess of Hertford, was the second surviving daughter of Henry Grey, 1st Duke of Suffolk and Lady Frances Brandon. She was the younger sister of Lady Jane Grey and older sister of Lady Mary Grey. Her maternal grandparents were Charles Brandon, 1st Duke of Suffolk and Mary Tudor, former Queen consort of France. Wikipedia
The definitive Wikipedia entry for Lady Catherine Grey. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Lady_Catherine_Grey
Lady Jane Grey , the unfortunate Queen of England for just nine days, wrote the above letter to her younger sister Catherine before her execution. www.tudorplace.com.ar/Bios/CatherineGrey.htm