‘Peter, turning round, sees the disciple whom Jesus loved following, he who also leaned back on his breast at the Supper and said ‘Lord, who is it who betrays you?'
John here makes clear that ‘the disciple whom Jesus loved' was a real person who did real things, and refers to only one identifiable person. How could he have made it more clear? And that person was a favoured one who was next to Jesus at the table. And he is there with Peter and the rest, one of the seven. It is quite clear that he is an Apostle, and a favoured one at that. Everything points to John even if we had no evidence outside the Gospel.