When Nuno Álvares saw that the assembled Portuguese force was disbanding and that each of the captains was returning to his own border region, he became very annoyed, as we have said. Being a young man of great courage who so desired to serve the king who had raised him, as well as to be known and have a good reputation, without speaking to anyone else, he thought about the outstanding quality of the upbringing that the king had given him and about the many favours his family had received from him. He also recalled the disservices that the Master [of Santiago] Fernando Osórez had done him in his kingdom and how the king did not hold so many men in his power that he could reply to them as his heart desired. He then thought of one son whom the master loved greatly; his name was Juan de Osórez. Nuno Álvares decided that he could challenge him to mortal combat, ten men against ten. He considered that if it should please God that he should kill him, he would cause great harm to the master, bearing in mind that he could not do otherwise. Should the opposite occur, he would regard as worthwhile any outcome God wished to give him, as it was in the service of his liege lord the king.

Without further delay, he gave effect to his thoughts and challenged Juan de Osórez, who was in Badajoz with his father, summoning him to a duel, stating in his letter to him, in words that were fitting in such a case, that he wanted a fight to the death, ten men against ten. Juan de Osórez was an honourable knight and a very brave one, and he gladly accepted the challenge, showing that it greatly pleased him by immediately choosing those who would be with him.

As soon as Nuno Álvares received his message that he was pleased they were to enter the field of battle, he was so happy that nothing else could have made him happier. He immediately set to work to select nine companions who with him would make up ten.