Who was Cardinal de Rohan? Describe his ancestry.

What book or story is this from?

its from the necklace that cost marie antoinette her head

From the text:

Louis, Cardinal de Rohan, prince-bishop of Strasbourg and head of the French church, was the gilded child of a gilded family. His family traced their lineage, with a little creativity, back to Conan Meriadoc, the mythical founder of Brittany. Rohan’s uncle was Louis XV’s drinking buddy; his aunt was governess to three kings of France.