Peter III of Russia
Empress Elizabeth arranged for Peter to marry his second cousin, Sophia Augusta Frederica (later Catherine the Great), daughter of Christian August, Prince of Anhalt-Zerbst and Johanna Elisabeth of Holstein-Gottorp. The young princess formally converted to Russian Orthodoxy and took the name Ekaterina Alexeievna (i.e., Catherine). They married on 21 August 1745. The marriage was not a happy one but produced one son, the future Emperor Paul, and one daughter, Anna Petrovna (20 December 1757 – 19 March 1759). Catherine later claimed that Paul was not fathered by Peter: that, in fact, they had never consummated the marriage. During the sixteen years of their residence in Oranienbaum, Catherine took numerous lovers, while her husband did the same in the beginning.
Pyotr Bagration
He was the alleged lover of Emperor Paul's daughter Catherine. In 1800 Paul recognized the title of "Prince ("Knyaz") Bagration" for Pyotr in Russia, and unexpectedly married him off to Countess Catherine Pavlovna Skavronskaya, the favorite niece of Grigory Potemkin and one of the Empress Maria's ladies-in-waiting. Bagration and Catherine had been casually involved, but the marriage was a failure. The young and lovely Catherine soon preferred traveling and, in 1805, fled to Vienna, where her salon and running affair with Prince Clemens von Metternich—who called her "the Naked Angel"—permitted her to serve as an important agent of Russian intelligence and diplomacy. Bagration was obliged by the emperor to claim their daughter, Marie-Clementine, as his own and to subsidize thousands of rubles of Catherine's debts. He had a reputation as a heavy gambler, as well, and was forced to sell estates to cover losses that rose as high as 80,000 roubles.