The Chronicon Mundi of Lucas Tudensis names "Adefonsum, Fredericum, Fernandum, Philippum, Henricum, Sancium, Emanuelem" as the sons of Fernando III King of Castile and his first wife. The Anales Toledanos record the birth 23 Nov 1221 of “el Infant D. Alfonso, fillo del Rey D. Fernando de Castiella…e…de la Reyna doña Beatriz, filla del Emperador de Alemaña”. The Chronicon de Cardeña names “Rey D. Alfonso” as son of “Rey D. Ferrando” and his wife “Doña Beatriz, la sobrina del Emperador de Alemaña”.
"Ferrandus…Rex Castelle et Toleti…cum uxore mea Regina Beatrice et filiis meis Alfonso, Frederico, Fernando" donated property at Villabañez to the church of Valladolid by charter dated 27 Apr 1226. "Ferrandus…Rex Castelle et Toleti…cum uxore mea Regina Beatrice et filiis meis Alfonso, Frederico, Ferrando, Henrico" donated the churches of Montealegre to the church of Valladolid by charter dated 25 May 1230. Alférez of his father Fernando III "el Santo" King of Castile 21 Aug 1242 to 22 Aug 1242.
He succeeded his father in 1252 as ALFONSO X “el Sabio” King of Castile, León, Galicia, Toledo, Badajoz, Cordoba, Murcia, Jaén and Sevilla. Immediately after his accession, he revived Castile's claim to Gascony and allied himself with Gaston VII Vicomte de Béarn. After the death in 1254 of Konrad IV King of Germany, King Alfonso claimed the duchy of Swabia (through his mother) and was supported by Pope Alexander IV writing to the Swabian nobility on 3 Feb 1255 and by Pisa under the treaty of Soria 18 Mar 1256. He attracted support from Brandenburg by the betrothal of his daughter to the eldest son of the Markgraf. He was elected ALFONSO King of Germany and King of the Romans at Frankfurt 1 Apr 1257 by Arnold Archbihsop of Trier, and the Saxon and Brandenburg rulers, but was unable to travel to Germany to stake his claim due to internal problems in Castile. King Alfonso ruined Castile financially while promoting his ambitions in Germany. His brothers Infantes don Enrique and don Felipe rebelled against him, the civil war lasting from 1271-1274. After the election of Rudolf von Habsburg as King of Germany in 1273, King Alfonso continued to press his claims to the Imperial crown and the Duchy of Swabia. He sent Castilian troops to northern Italy to help his son-in-law Guglielmo di Monferrato attack the vicar of Lombardy appointed by Charles I King of Sicily. Queen Violante abandoned him in 1275, fearing for her life after the death of their oldest son. Alfonso X King of Castile "con la Reyna doña Yolant mi muger y con nuestros fijos el Infante don Sancho fijo mayor y heredero, y con don Pedro, y D. John, y D. Jaymes" donated "la villa de Caztalla" to the Order of Calatrava by charter dated 1279. Alfonso X sponsored a compilation of laws known as “Las Pastido”. His younger son Sancho rebelled against him, deposed his father and had himself proclaimed King of Castile in 1282 by a Cortes at Valladolid. Alfonso X nominated his grandson Alfonso de la Cerda as his successor but his wishes were not respected.
The Chronicon Domini Joannis Emmanuelis records the death in Apr 1284 of “Rex Alfonsus in Hispali”. The Anales Toledanos record the death “pridie Non Apr” in 1284 of “Rex Alfonsus”. The Nobiliario of Pedro Conde de Barcelos records that "D. Alonso" died and was buried "en Sevilla". According to Szabolcs de Vajay, his viscera were buried separately at Murcia Cathedral. 1