On 21 April 1896, Prince Sizzo's succession rights were recognised by all members of the House of Schwarzburg. In addition, he was made a full member of the house and able to use the title of Prince of Schwarzburg. Following the agreement, Prince Sizzo became the
heir presumptive of
Schwarzburg-Rudolstadt, ahead of the Sondershausen princes, and third in line to
Schwarzburg-Sondershausen behind the reigning prince of Rudolstadt,
Prince Günther Victor, who was second and the brother of the reigning prince of Schwarzburg-Sonderhausen, Leopold, who was first (died in 1906). Following the death of
Prince Karl Günther of Schwarzburg-Sondershausen on 28 March 1909, the Sondershausen branch became extinct and the Schwarzburg principalities were united in a
personal union under Prince Günther Victor of Schwarzburg-Rudolstadt. Therefore, Prince Sizzo became the heir presumptive to the two principalities. However, his chances of succeeding were ended on 22 November 1918, when Prince Günther Victor abdicated following the
German revolution, which deposed all of the German monarchs. Following the death of Prince Günther Victor on 16 April 1925, Prince Sizzo succeeded him as head of the
House of Schwarzburg. His tenure as head of the house would not last long and less than a year later, Prince Sizzo died in
Großharthau with his only son,
Prince Friedrich Günther, succeeding him as head of the house and pretender to the Schwarzburg principalities. ==Marriage and children==