Seymour 's ambitions led to him being arrested and beheaded , after which Sudeley Castle became the property of Catherine 's brother William Parr , who was the Marquess of Nothampton . In 1549 , Seymour 's ambitions led him to being arrested and beheaded ; after which , Sudeley Castle became the property of Catherine 's brother , William Parr , Marquess of Northampton .