Queen Louise, 1710

Queen Louise. Painted by J.S. du Wahl. Louise of Mecklenburg-Güstrow was married to the crown prince of Denmark, Frederik IV, in 1695. Considering that marriages foremostly were nothing but political tools, this marriage fits into that category perfectly, and their relationsship was primarily centered on their obligation to produce legitimate offspring.

Oftentimes when a king had a sufficient number of male heirs, he would then choose to remarry, sometimes he would simply marry despite already being married, or lastly a king could of course entertain mistresses. This time around he could even choose his new spouse for his own reasons, be it love, looks, power  etc. Frederik IV did all of the above, having married during a marriage (the first one as early as 1703 was called Elisabeth Helene von Vieregg), remarried, and naturally he kept mistresses as well.