CREATE TABLE table_53880 ("Interregnum began" TEXT, "Interregnum ended" TEXT, "Duration" TEXT, "Count Palatine of Saxony" TEXT, "Count Palatine of the Rhine" TEXT)

What is the Interregnum ended for the person with a Duration of 3 months, 6 days?
SELECT "Interregnum ended" FROM table_53880 WHERE "Duration" = '3 months, 6 days'
SELECT "Interregnum ended" FROM "table_53880" WHERE "Duration" = '3 months, 6 days'