Answer
The Battle of Aljubarrota, fought in 1385, played a pivotal role in shaping Beatrice's claim to the Portuguese throne. The clash marked a turning point in the 1383-1385 Portuguese Interregnum, a period of political instability following the death of King Ferdinand I. The battle resulted in a decisive victory for the Portuguese forces led by John I, illegitimate son of King Pedro I, over the Castilian army supporting Beatrice's claim.