I found this article with a very good family-tree about the scandinavian royalhouse + the english royalhouse, we can see the relations between the familymember. (If you click on the picture it will be bigger:)
Dag Trygsland Hoelseth: Royal family tree in Dagsavisen 29 October 2012
Origininally I read articles about Josephine, the first wife of Napoleon I. I was surprised that she had two children before her marriage with Napoleon... And on the Wikipedia is written that the reigning houses of Belgium, Norway and Luxembourg also descend from her.
Joséphine de Beauharnais - Wikipedia, the free encyclopedia
Her grandchild was Joséphine Maximilienne Eugénie Napoléone, the wife of King Oscar I.
Josephine of Leuchtenberg - Wikipedia, the free encyclopedia
And the grandchild of this Joséphine Maximilienne Eugénie Napoléone is Prince Carl, the father of Princess Märtha (the mother of King Harald):
Prince Carl, Duke of Västergötland - Wikipedia, the free encyclopedia
I find it fascinating, that in the blood of Princess Ingrid-Alexandra "flows" the blood of Empress Josephine, the wife of Napoleon I.