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.
Henry III of Castile
In 1388, as part of the Treaty of Bayonne, he married Catherine of Lancaster in Palencia Cathedral. She was the daughter of John of Gaunt, the Duke of Lancaster, and Constance of Castile, a daughter of Peter the Cruel. This solved the dynastic conflict that had raged since the death of Peter the Cruel, secured the House of Trastámara, and established peace between England and Castile.