John Gill

Then Peter turning about,.... After he was risen, and was following Christ: seeth the disciple whom Jesus loved following also; by whom is designed John the Evangelist, and writer of this Gospel; who hearing Christ bid Peter follow him, rose up likewise, and went after him, in token of his willingness to serve him, and suffer for him too: which also leaned on his breast at supper; at the "paschal supper", as the Persic version here reads it: "and said, Lord, which is he that betrayeth thee?" This disciple had a peculiar share in the love of Christ, as man, and was admitted to great nearness and freedom with him, signified by his leaning on his breast; and who being so near his person, and allowed to use a liberty with him, everyone did not take, at the motion of Peter, asked our Lord at supper, who the person was he meant that should betray him; all this is said as descriptive of the disciple here spoken of, which leaves it without any doubt, that it was the Apostle John; and who, from Joh 21:2 appears to be one of this company, and is further confirmed at Joh 21:24.