Who is XXX's sister?
Edward Seymour, 1st Duke of Somerset
Edward Seymour, 1st Duke of Somerset, KG, (c. 1500 -- 22 January 1552) was the eldest brother of Queen Jane Seymour (d.1537), third wife of King Henry VIII (1509-1547) and mother of King Edward VI (1547-1553), the latter whom as his uncle and during his minority he served as Lord Protector of England in the period between the death of King Henry VIII in 1547 and his own indictment in 1549.
Jane Seymour