Paul I of Russia
Paul remained overshadowed by his mother for most of his life. His reign lasted four years, ending with his assassination by conspirators. He adopted the laws of succession to the Russian throne—rules that lasted until the end of the Romanov dynasty and of the Russian Empire. He also intervened in the French Revolutionary Wars and, toward the end of his reign, added Kartli and Kakheti in Eastern Georgia into the empire which was confirmed by his son and successor Alexander I.
Russian interregnum of 1825
Alexander I of Russia, the elder of four sons of Paul I, had no male issue; his legitimate daughters died in infancy. According to the 1797 Pauline Laws his childless brother Constantine had been heir presumptive since Alexander's accession. The third brother, Nicholas, followed him in the order of succession. Constantine and his legitimate wife Juliane of Saxe-Coburg-Saalfeld separated in 1799. Juliane returned to Germany and resisted any proposals to restore the family. Constantine, engaged in the action of the Napoleonic Wars, did not attempt a formal divorce until meeting Joanna Grudzińska. Their love affair that began in 1815 compelled Constantine to divorce Juliane and marry Joanna.