Yes indeed, King Alphonso almost succeeded to the throne of his father, Edward I. If you go to this page, you will learn about Alphonso, Earl of Chester (1273-1284) the ninth child of King Edward I and Eleanor of Castile. He was apparently named after his maternal uncle, King Alphonso X of Castile, and there was a time when he was first in line to the throne of England. He died, just short of 11 years of age, not long after the birth of his parents’ next son, another Edward, who was to become Edward II of England.
At the age of 10 Alphonso was betrothed to Margaret, daughter of the Count of Holland, but died a few months before the wedding. This psalter was being prepared, and the illustration below, showing the bridal couple’s arms, is taken from it.
Most of the above information has been taken from History UK (see link above). I do not claim the kudos. You can read more about Alphonso here and about the roll from which the portrait of Alphonso is taken, at the British Library.