There was a legal impediment to the marriage of his daughter with her cousin, the Duke of Savoy. The so-called «Law of the Cortes of Lamego» prevented the marriage of an heiress with a foreign prince. This alleged document became fundamental law of the Realm in 1640. The Cortes, called on 1 November 1679, proceeded with the derogation. By then the ambassador of Savoy, the Marquis of Ornano, had come to Lisbon to celebrate the marriage by proxy. But it would all turn ineffective to the extent that the embassy of the Duke of Cadaval, sent to Turin in May 1682, did not reach or did not finish the project, by pressures, perhaps, of Louis XIV on the dynasty of Savoy.