Mary Seymour (30 August 1548 - c. 1550?), born at her father’s country seat, Sudeley Castle in Gloucestershire, was the only daughter of Thomas Seymour, Baron Seymour of Sudeley, and Katherine Parr, widow of Henry VIII of England. Although Katherine was married four times, Mary was her only child. Complications from Mary's birth would claim the life of her mother on 5 September 1548, and her father was executed less than a year later for treason against Edward VI.
In 1549, the Parliament of England passed an Act (3 & 4 Edw. 6 C A P. XIV) removing the attainder placed on her father from Mary, but his lands remained property of the Crown.
As her mother's wealth was left entirely to her father and later confiscated by the Crown, Mary was left a destitute orphan in the care of Katherine Willoughby, Duchess of Suffolk, who appears to have resented this imposition. After 1550 Mary disappears from historical record completely, and no claim was ever made on her father's meagre estate, leading to the conclusion that she did not live past the age of two.
Victorian author Agnes Strickland claimed, in her biography of Katherine Parr, that Mary Seymour did survive to adulthood, and in fact married Sir Edward Bushel, a member of the household of Queen Anne of Denmark, consort to King James VI of Scotland and I of England. Strickland's theory suggested that the Dowager Duchess of Suffolk, after her marriage to Richard Bertie in 1553, and before she fled England during the Marian Persecutions in or after 1555, she arranged Mary's marriage to Bushel. The problem with this theory is that Mary would have been aged six at the time.