To preserve Portugal as an ally, Juan, in the second year of his reign, consented or proposed to marry his infant son Henry with Beatrice, presumptive heiress of the Portuguese crown. This princess, who was in her tenth year, had been promised to Frederick, brother of the Castilian king; but the superior pretensions of Henry induced the Portuguese monarch to prefer the latter for a son-in-law. One condition of the projected marriage was that, in case either of the young betrothed died without issue, the other should inherit the states of the deceased. So fair a prospect of uniting the two crowns could not fail to be agreeable to the two sovereigns. Notwithstanding this solemn treaty, Ferdinand of Portugal secretly resolved to make war on Castile; and, with the view of strengthening himself by the alliance of the duke of Lancaster, he despatched a trusty messenger to obtain the co-operation of that prince, who readily promised it. [Sidenote: [1380-1385 A.D.]] Juan, who was soon acquainted with the league, resolved to anticipate his enemy: off Cape St. Vincent his fleet triumphed, in 1381, over that of Ferdinand; and Almeida was forced to submit to him. The arrival from England of the earl of Cambridge, brother of the duke, with five hundred men-at-arms, and as many archers, roused the courage of the Portuguese, but did them little service. As the allies could obtain no money from Ferdinand, they did not scruple to lay their hands on whatever they pleased: hence the distrust and dislike which arose between them and the natives, and which neutralised the little success obtained by their combined arms.[44] Wearied alike with his allies and the war, Ferdinand, in 1382, solicited and obtained peace, and the English returned home. The death of the queen of Castile leaving Henry a widower, Ferdinand offered him the princess Beatrice, who had been successively promised to his brother, to his two sons, and even to the son of the earl of Cambridge; on condition, however, that the issue of the marriage, whether male or female, should be the sovereign of Portugal, and that he himself should have no share in the administration so long as Leonora, the Portuguese queen, should survive Ferdinand. This condition, so characteristic of Portuguese dislike of Castilian sway, did not prevent Juan from marrying the princess. Ferdinand died the very year of this marriage; and his death opened the door to new hostilities.