Mary was the daughter of Thomas Boleyn, Earl of Wiltshire and Ormond, and his wife, Elizabeth Howard. She was the granddaughter of Thomas Howard, 2nd Duke of Norfolk, and sister of Queen Anne Boleyn and George Boleyn, Lord Rochford. At some point, she had been King Henry VIII's mistress, but nothing is known of their relationship.
At the time of her death, Mary was married to William Stafford, but had previously been married to William Carey, a member of Henry VIII's Privy Chamber and an Esquire of the Body. She had two children during the course of her first marriage: Catherine and Henry. Carey died of sweating sickness in 1528 and in 1534 Mary married Stafford secretly and without her family's permission.
Here is my playlist of Mary Boleyn videos:
Also on this day in Tudor history...
Image: A portrait of a woman thought to be Mary Boleyn from the collection at Hever Castle.