The Treaty of Trentschin was concluded on 24 August 1335 between King Casimir III of Poland and King John of Bohemia as well as his son Margrave Charles IV. The agreement was reached by the agency of Casimir's brother-in-law King Charles I of Hungary and signed at Trencsén Castle in the Kingdom of Hungary (present-day Trenčín, Slovakia). It initiated the transfer of suzerainty over the former Polish province of Silesia to the Kingdom of Bohemia, whereafter the Duchies of Silesia were incorporated into the Bohemian Crown.