Matthew Poole and continuators on John 18:16

16 But Peter stood at the door without. Then went out that other disciple, which was known unto the high priest, and spake unto her that kept the door, and brought in Peter .

This further confirmeth the conjecture of those, who think that other Disciple was none of the Apostles, but a favourer of Christ, that lived in Ierusalem, and was of some repute either for estate or place; so as he had not onely an acquaintance with the High Priest, but also with his family; and could gain admittance into his Palace, not onely for himself, but also for his friend.

Marginal references: Mat. 26.58.