Excerpts from Books and Wikipedia
"Forces commanded by King John I of Portugal and his general Nuno Álvares Pereira, with the support of English allies, opposed the army of King John I of Castile with its Aragonese, Italian and French allies at São Jorge, between the towns of Leiria and Alcobaça, in central Portugal. The result was a decisive victory for the Portuguese, ruling out Castilian ambitions to the Portuguese throne, ending the 1383–85 Crisis and assuring John as King of Portugal. Portuguese independence was confirmed and a new dynasty, the House of Aviz, was established." [Wikipedia] "John of Gaunt intended to seize the throne of Castile, and to do so, he negotiated an alliance between England and the king of Portugal. . . . But the war turned into an assertion of Portuguese independence against Castilian might, of John of Aviz's right to rule as sole sovereign against Castilian ambitions to control Portugal. In August of 1385, John of Aviz defeated the French-Castilian forces at the Battle of Aljubarrota, bringing a crashing end to Castilian attempts to reclaim Portuguese land. The victory made John of Aviz a hero in the eyes of his people and strengthened his claim on the throne. But it did nothing for John of Gaunt."