Who was the heir apparent to the English throne who never became king, allowing his younger brother to succeed to the throne in 1307?
Edward II of England:  Edward succeeded to the throne in 1307, following his father's death. Alphonso, Earl of Chester: Alphonso or Alfonso (24 November 1273 – 19 August 1284), also called Alphonsus and Alphonse and styled Earl of Chester, was an heir apparent to the English throne who never became king.
Alphonso