Original: When Figaro declares himself to be of noble birth and that he was stolen from his parents when he was a baby, the subsequent discussion reveals that Figaro is the long-lost illegitimate son of Bartolo and Marcellina.
Simplified: When Figaro says that he himself is of noble birth and that he was stolen from his parents when he was a baby, it then turns out that Figaro is the long-lost illegitimate son of Bartolo and Marcellina.