I don't suppose this is an original thought but thinking about John's Gospel, its author and the way in which it is sooo different to the Synoptic Gospels, I am taken by the relative parallel between John 1: 18 and John 13:23
'No one has ever seen God. The only begotten God, the one being in (or near) the breast (kolpon) of the Father, that one brought out the knowledge of him (exegesato).'
'One of his disciples, whom Jesus loved, was lying close to the breast (kolpo) of Jesus.'
How do we know who God is (according to the Gospel of John)? Through the knowledge shared with us by the one (the Son) being in or near the breast of the Father.
How do we know about the Son (and thus about what the Son knows about the Father)? Through knowledge shared with us by the one (the author, see John 21:24) being in or near the breast of Jesus.
In other words, despite the immense differences between the Synoptics and the Fourth Gospel, we cannot dismiss the Fourth Gospel as some kind of fictional creation because its claim is that it is written by one who was as intimate with Jesus the Son as the Son was intimate with the Father.
We may not know the name of the author, or, if the name is John, we may not know which John the name belongs to, but we know something very significant about the author: he was an intimate of Jesus. One question then is whether this intimacy was that of one of the Twelve or another disciple. Generally the signs in the Fourth Gospel point to 'another disciple'; and generally the Synoptics give signs that there were other disciples of Jesus than those named therein (e.g. the host of the last supper).