Who is Alfredo from The Finkler Question and what is their importance?

Alfredo, the son of Julian and Josephine, is nicknamed Alf. He plays the piano in hotels which is how he develops an uneasy friendship with Sam after seeing Sam at a hotel with his mistress. He informs Rodolfo and their mothers about Julian's mugging and his decision that he is Jewish. He goes on vacation to Italy with Julian and Rodolfo where he joins his brother in mocking their father for his belief that he is Jewish. Alfredo also sits across from Libor on the train to Eastbourne, but they do not recognize one another since Julian had never introduced them.