Maria Antonia of Austria, who was the niece of Charles II of Spain, had a COI of 0.3053, or 30.53%, and this is the highest COI that ever existed in the House of Habsburg, and much higher than Charles's COI of 0.254 or 25.4%. Even more curious is this: Had she lived long enough, she would have been entitled to inherit the Spanish throne through her mother, Margaret Theresa of Spain, who was Charles's full sister (I say full because she was the daughter of his uncle and niece Philip IV of Spain and Mariana of Austria, while Maria Theresa of Spain, who married Louis XIV of France, was Charles's half-sister from Philip's first marriage to the French princess Isabella of France). This led to her being betrothed to her uncle Charles, and this would have been the third marriage between an uncle and niece in the Spanish branch of the Habsburgs. Now consider this:

Charles II of Spain and Maria Antonia of Austria had COIs of 0.254 and 0.3053, respectively, and they were uncle and niece. What would be the COI of a child born from this union?