On September 24, 1749, a ‘superb black man’, well dressed, speaking and writing French with surprising resourcefulness, was arrested in the port of Morlaix in Finisterre, often frequented by Breton corsairs. Arrested after a fight in a tavern in the city, the person was identified by the Morlaix police as someone wanted in several ports of Brittany for having left many unpaid bills and distributing counterfeit bills of debt and exchange. During the police interrogation, the defendant surprisingly identified himself as the ‘Prince of Macao’ and the elder son of its king, the ‘Grand Lord of Macao’. To the astonishment of the officials, he signed his statements with elegance as ‘Rodolfo, Deo Gratias Princeps ad Macao’. This article investigates this well-documented criminal case and then tries to understand the contexts and reasons for this strange falsification of a supposed ‘Prince of Macao’ in mid-18th-century France.