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.
Catherine Parr
Catherine married Henry VIII on 12 July 1543 at Hampton Court Palace. She was the first Queen of England also to be Queen of Ireland following Henry's adoption of the title King of Ireland. Catherine and her new husband shared several common ancestors making them multiple cousins. By their mothers they were third cousins-once-removed sharing Sir Richard Wydeville and Joan Bedlisgate; by Henry's mother and Catherine's father they were third cousins once removed sharing Ralph Neville, 1st Earl of Westmorland and Lady Joan Beaufort; and by their fathers they were double fourth cousins once removed sharing Thomas Holland, 2nd Earl of Kent and Lady Alice FitzAlan and John of Gaunt, 1st Duke of Lancaster and Katherine Swynford.