Pr. Ferdinand of Prussia (1730-1813) married his niece Luise, Margravine of Brandenburg-Schwedt (1738-1820)
I guess there must be other cases.
These (to me, and many others, I imagine) shocking marriages between uncles and nieces seem to have happened only in Catholic ruling families, or am I wrong? I suppose they were all given dispensations from the Church, which seems...very wrong. I say this as a Catholic myself, by the way.
Also, Duke Francesco IV of Modena married the eldest daughter (Princess Maria Beatrice of Savoy) of his sister, Archduchess Maria Theresia of Austria-Este. The present-day Jacobite claimant (HRH Franz, The Duke of Bavaria) descends from this marriage. Given the fact that uncle-niece marriages are illegal in the UK, however, some contend that the rightful claimant is Prince Pedro of Bourbon-Two Sicilies (who descends from Princess Maria Teresa of Savoy, younger sister of Maria Beatrice). There is some logic to this contention, since one can exclude entire lines from the British succession, on the grounds that an ancestor was born out of lawful wedlock.
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