King in Prussia
When Frederick William died in 1688, he was followed by his son Frederick, third of that name in Brandenburg. As the lands that had been acquired in Prussia were outside the boundaries of the Holy Roman Empire, Frederick assumed (as Frederick I) the title of "King in Prussia" (1701). Although his self-promotion from margrave to king relied on his title to the Duchy of Prussia, Brandenburg was still the most important portion of the kingdom. However, this combined state is known as the Kingdom of Prussia.