The House of Schwarzburg is one of the oldest noble families of Thuringia. Upon the death of Prince Friedrich Günther in 1971, the headship of the house passed under Semi-Salic primogeniture to his elder sister, Princess Marie Antoinette of Schwarzburg who married Friedrich Magnus V, Count of Solms-Wildenfels. The House of Schwarzburg subsequently became a personal union with the House of Solms-Wildenfels. Reigning over the County of Schwarzburg and founded by Sizzo I of Schwarzburg (died 1160), the family split in the 16th century into the lines of Schwarzburg-Sondershausen and Schwarzburg-Rudolstadt, with the Sondershausen dying out in 1909.