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.
Saint Petersburg
The names of Saints Peter and Paul, bestowed upon original city's citadel and its cathedral (from 1725—a burial vault of Russian emperors) coincidentally were the names of the first two assassinated Russian Emperors, Peter III (1762, supposedly killed in a conspiracy led by his wife, Catherine the Great) and Paul I (1801, Nicholas Zubov and other conspirators who brought to power Alexander I, the son of their victim). The third emperor's assassination took place in Saint Petersburg in 1881 when Alexander II fell victim to narodniki (see the Church of the Savior on Blood).