Paul I of Russia
Paul I (; "Pavel Petrovich") ( – ) reigned as Emperor of Russia between 1796 and 1801. Officially, he was the only son of Peter III and Catherine the Great, though Catherine hinted that he was fathered by her lover Sergei Saltykov, who also had Romanov blood, being a descendant of the first Romanov tsar's sister, Tatiana Feodorovna Romanova.
Nicholas I of Russia
With two older brothers, it initially seemed unlikely Nicholas would ever become Tsar. However, as Alexander and Constantine both failed to produce sons, Nicholas remained likely to rule one day. In 1825, when Alexander I died suddenly of typhus, Nicholas was caught between swearing allegiance to Constantine and accepting the throne for himself. The interregnum lasted until Constantine, who was in Warsaw at that time, confirmed his refusal. Additionally, on 25 (13 Old Style) December, Nicholas issued the manifesto proclaiming his accession to the throne. That manifesto retroactively named 1 December (19 November Old Style), the date of Alexander I's death, as the beginning of his reign. During this confusion, a plot was hatched by some members of the military to overthrow Nicholas and to seize power. This led to the Decembrist Revolt on 26 (14 Old Style) December 1825, an uprising Nicholas was successful in quickly suppressing.