The idea that Agnes Edwards was a mistress of Henry VIII, and that her son Reverend Richard Edwardes, I was an illegitimate son of Henry VIII, is common among some Edwards descendants. The claim was popularized by David D. Edwards in The Edwardes Legacy (1992) and might have originated as an original theory by Mr. Edwards. He claimed that it is "whispered among some Tudor researchers that Agnes was mistress to King Henry VIII of England and that the son Richard was fathered by King Henry and not by William."
However, the idea that Henry VIII was the father of Richard Edwardes was discredited in Kelly Hart’s, The Mistresses of Henry VIII (2009). She categorized the claim as rumor. saying, " This rumour seems to have originated from the Edwardes family themselves and not from contemporary source. Much of our (more dubious) information comes from family histories."
“There are also suggestions that Richards Edwardes was Henry’s son. The evidence rests on him receiving an Oxford education that his family could not have afforded. There are many possible explanations for this: he could have had a benefactor, a scholarship, or perhaps his mother was the mistress of a rich man. Richard or his family may have impressed someone influential. Perhaps it was his father who paid – but there were many men who could have afforded to pay this and there is no reason to assume that it was Henry VIII. Richard Edwardes has many descendants who believe he was Henry’s son. This rumour seems to have originated from the Edwardes family themselves and not from contemporary source. Much of our (more dubious) information comes from family histories.
Edwardes’ mother, Agnes Blewitt, was not a courtier. She was from Somerset and is unlikely to have met Henry; he may have had affairs with low-born women, but they were unlikely to have lasted long. Mistresses needed to be able to dazzle at courtly accomplishments and this usually meant having had an aristocratic upbringing. It could cause offence to target wives and daughters of the highest in the land, but the king was also not expected to keep the company of women who were too far his social inferiors. A commoner may have held Henry’s attentions long enough for a casual fling and perhaps to conceive a child. Yet Henry may have considered his social inferiors for long-term mistresses, as he happily picked low-born ministers.
Edwardes was a poet, musician and composer who spent some time at Elizabeth’s court. He married Helene Griffith, which does not seem to have been an advantageous marriage. They had one son, William, who continued the Edwardes line by having sixteen children. Richard Edwardes died in 1566, three years after his marriage, and there is no evidence that links him to Henry VIII during their lifetime. Nevertheless the rumours persist.” (pp. 77-78).
http://www.thetudorswiki.com/page/MISTRESSES+of+the+King