A good gossip about a baby: whose was it?

Miss Williams Wynn is today have a good gossip about the postumously born son of the Duc de Berri (who was assassinated in 1820; also known as Berry). Usually doubts are about fatherhood, but this one is a doubt about motherhood - was he actually the son of the duke's English mistress?

Before that, she had a lovely tale about a quality imposter, who made himself a bishop. Although he ended on the galleys in the end ...