user: Question: Which father had William IV as a husband?
Columns: ['Image', 'Father', 'Birth', 'Ceased to be Duchess', 'Death', 'Husband']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Kunigunde of Austria', 'Frederick III, Holy Roman Emperor ( Habsburg )', '16 March 1465', "18 March 1508 husband's death", '6 August 1520', 'Albert IV']
SQL:

assistant: SELECT "Father" FROM "Table" WHERE "Husband" = 'William IV';