See the notes at Matthew 26:57-58.
Another disciple - Not improbably John. Some critics, however, have supposed that this disciple was one who dwelt at Jerusalem, and who, not being a Galilean, could enter the palace without suspicion. John, however, mentions the circumstance of his being known to them, to show why it was that he was not questioned as Peter was. It is not probable that any danger resulted from its being known that he was a follower of Jesus, or that any harm was meditated on them for this. The questions asked Peter were not asked by those in authority, and his apprehensions which led to his denial were groundless.