Alfonse Goldstein, oldest of the Goldstein brothers, is Klaus and Elias' older brother. He is also known for being the "disgrace" of the family, the exact reasons are yet to be specified.
In Klaus main route I, Alfonse was said to be engaged with Elaine.
In Season 6 is revealed that Alfonse is a prefect for the Day Class. Quite knowledgeable on magic potions, he previously joined the ministry’s research trip, just recently returning to Gedonelune.