Isabel's son and heir Alfonso XII first wife was the infanta Maria Mercedes a daughter of his mother's younger sister.
They were also paternal first cousins and their maternal grandparents had been first cousins as well.
To top it all their maternal grandmother was a full sister of their fathers.....
Emperor Fanz Joseph I. of Austria and Duchess Elisabeth in Bavaria where maternal first cousin as their mothers where both daughters of King Maximilian I. of Bavaria
Prince Heinrich of Prussia and Princess Irene of Hesse-Darmstadt also spring to mind. Their mothers were both daughters of Queen Victoria of the UK.
The oldest and youngest from Anna Pavlovna's and Willem II's children married a maternal first cousin.
The oldest (Willem III) married Sophie of Wurttemberg daughter of his mother's deceased sister Catharina Pavlovna, queen of Wurttemberg.
The youngest (Sophie of the Netherlands) married Karl Alexander of Saxe-Weimar-Eisenach son of Maria Pavlovna an other of the 6 daughters from Paul Petrovich marriage to Maria Feodorovna (born Sophia Dorothea of Wurttemberg).
I know that Infanta Isabel of Portugal (granddaughter of Ferdinand and Isabel of Spain) married her first cousin, Holy Roman Emperor Carlos V. A more recent example of maternal parallel cousins marrying would be the Grand Duchess Charlotte of Luxembourg and Prince Felix of Bourbon-Parma. Can anybody name other examples in history of couples whose mothers were sisters?
As for agnatic cousins, I'm sure there are plenty of more examples. Such unions have occurred everywhere, from the UK (e.g. grandchildren of Frederick, Prince of Wales), Wuerttemberg, and Bavaria, to name just a few examples. Can anybody provide a list of these as well?
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