House of Mecklenburg
Around 1711, a treaty was signed between the Dukes of Mecklenburg and the Elector of Brandenburg through which the elector was recognized as the next heir of Mecklenburg after the male lines of the genealogical house of Mecklenburg. Thereby the electors, later kings of Prussia, regarded themselves as having become members of the House of Mecklenburg and started to use its titles, e.g. Duke of Mecklenburg, among their own titulary.