CREATE TABLE table_26519 ("Co-king" CLOB, "Relationship to Monarch" CLOB, "Crowned" CLOB, "Co-kingship ceased" CLOB, "Reason" CLOB, "Monarch" CLOB)

Name the monarch for 13 october 1131
SELECT "Monarch" FROM table_26519 WHERE "Co-kingship ceased" = '13 October 1131'
SELECT "Monarch" FROM "table_26519" WHERE "Co-kingship ceased" = '13 October 1131'