This article addresses the long-controversial dating of the cadenza with flute in the mad scene of Donizetti’s Lucia di Lammermoor. New manuscript sources indicate that the famous cadenza dates not from the first half of the nineteenth century, as musicologists had assumed, but from 1889, when it was added to the opera for Nelly Melba’s performances at the Palais Garnier, Paris. The cadenza was most likely composed by Melba’s teacher Mathilde Marchesi to showcase the light voice and virtuosic technique of her student. Once introduced, the cadenza with flute decisively altered the impact and reception of the mad scene. In the first two decades after the opera’s 1835 première, the mad scene had not been particularly popular, perhaps because it contravened contemporary Italian taste for mad scenes featuring docile, virginal heroines. By the fin de siècle, however, the mad scene was regarded as the highlight of the opera, the excesses of the cadenza resonating with the new vogue for violent and hysterical heroines on the operatic stage.