Queen Isabel II of Spain and her husband, King-Consort Francisco were first cousins and cousins several times over.
Their fathers were brothers
Their mothers were sisters
Their maternal grandparents were first cousins
Their maternal grandmother was a sister of their fathers
Their maternal grandfather was a first cousin of their fathers.
Everybody knows that there are four ways in which such unions are possible, and there have been plenty of occurrences of all types, throughout European royal history --
1) The father are brothers (e.g. Prince Ludwig and Princess Irmengard of Bavaria, in 1950; to the best of my knowledge, this was the last time such a thing happened)
2) The mothers are sisters (e.g. The Grand Duchess Charlotte of Luxembourg and her consort, Prince Felix of Bourbon-Parma, in 1919; again, I believe this was the last occurrence of such a union)
3) His father and her mother are brother and sister (e.g. Grand Duke Kirill Vladimiovich of Russia and Princess Victoria Melita of Edinburgh, in 1905; I'm not sure if this was the last such example)
4) Her father and his mother are brother and sister (e.g. Grand Duke Ernst of Hesse-Darmstadt and the same Princess Victoria Melita of Edinburgh, in 1894; again, I'm not sure if this was the last such example)
Anyhow, I was just wondering if anybody knew which type of first cousin marriage has been the most common, in European royal history. Surely somebody would have statistical data on the matter.
Also, are my examples correct, about the last time a particular type of cousin marriage occurred? Like I said, I'm a little murky about the latter two scenarios; even with the first two, there could be more recent examples.