She became the first wife of Sir Edward Seymour, who went on to become the first Duke of Somerset of a new creation, Lord Protector of England and the uncle of King Edward VI, after his sister Jane married King Henry VIII.
A 17th-century marginal note to copy of Vincent's Baronage at College of Heralds alleged that she had had an affair with her father-in-law, Sir John Seymour.
The will was challenged by Sir Edward Seymour in 1531, on the basis that his father-in-law was not of sound mind.
In 1535, Sir Edward Seymour married his second wife, Anne Stanhope, indicating that Catherine Fillol had probably died no later than early 1535.
When he was later created Duke of Somerset, his children by his first marriage were still considered legitimate, but the patent of nobility provides that the dukedom is to descend first to his heirs by Anne, and only in the event of the failure of that line to his heirs by Catherine.