Leonor persuaded her brother João Afonso Telo 6th Count of Barcelos and "Alcaide-Mór" (noble magistrate) of Lisbon, to insinuate the idea in the mind of the Infante that his marriage to her daughter, the heiress presumptive Beatrice (who was promised to John I of Castile), would find favour with the people and clear his way to the throne. With the false imputation that his present wife María had been unfaithful to him, transmitted by Leonora through John Alfonso, Infante John became so enraged that he stabbed María in Coimbra. In one single coup, Leonor Teles got disentangled of her sister and brought such opprobrium upon the name of her brother-in-law, that his hopes of succeeding to the throne were much diminished.