Entry taken from the book The Plantagenets
Two of the best-known monarchs of the Middle Ages in Europe were Alfonso X the Wise of Castile and Edward I of England, known as the Hammer of the Scots. In the blog and in some collaboration on other pages there are several entries dedicated to the famous English monarch who subdued Wales and battled with the Scots William Wallace and Robert the Bruce. Below I link some of these entries that serve to give an idea of the dimension that this English king reached.
Edward I of England v. Llewelyn, Prince of Wales.
Edward I, Wales and the Arthurian legends.
The origin of the title Prince of Wales to designate the heir to the English throne.
The birth of the myth of William Walllace.
There is a link between the two sovereigns that is little known and that took place in Burgos in 1254 when Alfonso X was at the height of his reign and Eduardo was only a prince barely fifteen years.
In the 13th century, the English kings were the lords of various territories on French soil, including Gascony. Normally the disputes over the domain of these territories were with the kings of France.
But in 1254, the dispute over Gascony was not with the King of France, but with Alfonso X of Castile. Gascony had been part of the dowry of the wife of King Alfonso VIII, the English princess Eleanor Plantagenet and, although that dowry was never made effective, since then the question of the right of Eleanor's descendants in the Castilian throne over that territory, an issue that Alfonso X set out to take up again, which caused a conflict with the English king, Henry III.
To solve the problem, and so that the young son of the English king, Prince Edward, would be hardened in government tasks, his father sent him to head the English delegation that traveled to Gascony. Finally, it was agreed that Alfonso would renounce his claims to Gascony and that in exchange the marriage between the English prince Edward and the sister of the King of Castile, named Leonor, would be arranged. 
That was the reason why the English delegation He traveled from Gascony to Castile and settled in the beautiful town of Burgos. King Alfonso insisted on ordering Prince Edward a knight in the place in the Castilian capital where this ceremony was traditionally held for the infantes of Castile:the Monastery of Las Huelgas, where the young prince's grandfather's sister was also buried. English, Leonor Plantagenet, origin of the conflict.
Thus a great monarch like Alfonso X the Wise of Castile knighted a fifteen-year-old boy destined to become another of the great European monarchs of the Middle Ages, Edward from England.
The third son of the marriage between Edward of England and Eleanor of Castile was baptized with the name of Alfonso and for years he was the heir to the throne. If he had not died before his father, more than one English king would have borne the Castilian name of Alfonso.
Source:Marc Morris Edward I, a great and terrible king.