The Castilian Civil War was a war of succession over the Crown of Castile that lasted from 1351 to 1369. The conflict started after the death of king Alfonso XI of Castile in March 1350. It became part of the larger conflict then raging between the Kingdom of England and the Kingdom of France: the Hundred Years' War. It was fought primarily in Castile and its coastal waters between the local and allied forces of the reigning king, Peter, and his illegitimate brother Henry of Trastámara over the right to the crown.