When his father died, his grandmother became regent and ruled
          wisely until her death in 1322. Alfonso XI assumed the sovereignty in
          1324 at the age of thirteen and a few years later mounted a campaign
          against the Moors of Granada, culminating in the battle of Salado
          which inflicted enormous losses on them. It is said to have been the
          first battle in Europe at which cannon were used.
                In 1328 he married Maria of Portugal but his heart had already
          been won by Dona Leonor de Guzman, a young widow of noble birth and
          acknowledged to be the most beautiful woman in the kingdom, with
          intellectual abilities to match. She was to be Queen of Castile in all
          but name throughout Alfonso's reign and bore the King a large family.
          Queen Maria was shamefully neglected and virtually completely
          abandoned after giving birth to two sons, of whom only the younger
          survived. She bided her time and brooded on her revenge.
                In 1330 he was the first European sovereign to found a royal
          order of chivalry, the Order of the Band. Intended to enhance his own
          reputation as a patron of the chivalrous ideal, the idea was soon
          copied by Edward III of England when he founded the Order of the
          Garter.
                Alfonso XI won a great victory against the Moors at Tarifa in
          1340 and next laid siege to Algeciras which surrendered in March 1344.
          A ten-year truce was made between Granada and Castile, but Alfonso XI
          soon found a pretext to break it; he was besieging Gibraltar when the
          Black Death overtook his camp and he became one of its victims in
          March 1350.
                No sooner was Alfonso XI dead than Leonor was arrested on the
          Queen's orders, conveyed to the Castle of Talavera, and there
          strangled. At the same time all the members of her family were
          subjected to a virulent persecution.
 

Source: Leo van de Pas