John 18:15 - Coke's Commentary on the Holy Bible

And so did another disciple:— This, as we have before observed, is supposed to have been St. John himself. See on Matthew 26:69 and Luke 22:54. Grotius however is of opinion, that this disciple was not one of the twelve, but rather an inhabitant of Jerusalem; possibly the person at whose house our Lord ate the paschal supper. Whitby likewise thinks it was not John. These authors found their opinion on this circumstance, that the twelve being Galileans, and men of mean stations, could not any of them be so well acquainted in the high-priest's family, as to procure admission for a friend at a time of so much business. However, when we consider that St. John was to write a history of Christ's life, it will appear very proper, but by no means necessary, that in the course of Providence he should have an opportunity afforded him of being an eye-witness of this most solemn scene before the council.