Jane was born in 1508 in Wulfhall, England. She was the eldest child of Sir John Seymour and Margaret, daughter of Sir John Wentworth. Through her maternal grandfather, she was a descendant of King Edward III's son Lionel of Antwerp, 1st Duke of Clarence. Because of this, she and King Henry VIII were fifth cousins. She shared a great-grandmother, Elizabeth Cheney, with his second and fifth wives, Anne Boleyn and Catherine Howard.