CREATE TABLE table_6453 ("Birth" TEXT, "Marriage" TEXT, "Became Duchess" TEXT, "Ceased to be Duchess" TEXT, "Death" TEXT, "Spouse" TEXT)

What is the Spouse of the Duchess that has a Death on 6 april 1780?
SELECT "Spouse" FROM table_6453 WHERE "Death" = '6 april 1780'
SELECT "Spouse" FROM "table_6453" WHERE "Death" = '6 april 1780'