Lettice Knolleys who Robert married was Elizabeth's first cousin once removed since Lettice was the granddaughter of Mary Boleyn the sister of Elizabeth's mother Anne. Lettice also could have been Elizabeth's niece since Mary Boleyn had an affair with Henry VIII and it is possible that Mary's daughter and the mother of Lettice was Henry's daughter as well.
After Charles says he doesn't want to be King Catherine sends for her younger son Henry. He is a young boy (who would have been about 10 in real life) with dark hair and eyes. In season 4 however which takes place very shortly afterward he is played by blonde haired blue eyed actor Nick Slater who was in his late 20s.