When in 374 Ambrose was elected bishop of Milan and baptized, Simplician became his teacher of doctrine. Ambrose used to call Simplician father, as a sign of spiritual relationship. Probably in this period Simplician moved to Milan where he remained.
In 374, when Ambrose was elected bishop of Milan and baptized, Simplician acted as his spiritual teacher. Ambrose referred to Simplician as father, signifying a strong spiritual relationship. It is probable that during this time, Simplician relocated to Milan and continued residing there.