Some say she was his mistress while Henry was married to Queen Catherine of Aragon.
"King Henry the VIII is said to have fathered a son with her, whom was born after her marriage to William Edwards. She and William named the son Richard Edwards."
If you put Agnes Blewiit:Henry VIII in a search tool such as google you will see many articles/stories that state this supposed relationship and can read much more.
Example below:
http://home.comcast.net/~kenconway/familytree/kinghenry.htm