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Mary's mother Catherine who died from childbirth complications soon after her birth

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, 1st Baron Seymour of Sudeley, and Catherine Parr, widow of Henry VIII of England. Although Catherine 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.

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, a, leading to the conclusion that she did not live past the age of two..

Catherine Parr's relationship with Thomas Seymour