I've no evidence it's true, but it's the tradition of at least some of the Church, and I think it's a better story. And, as the old quantum scientists knew, sometimes it's the more beautiful story that's the true one.
And that is that the author of John's Gospel was the son of Zebedee, was the disciple whom Jesus loved, was the writer of the Johannine epistles, was the exile on Patmos.
A form of martyrdom, to be sure. To be cast on that island, knowing that all those he had known and loved - Peter, Andrew, his brother James, Jesus's mother - all were gone. Many killed, in the name of Jesus, and John left all to himself, an old man, waiting. Always waiting.
He knew, in his long life, the terror of Babylon. He knew the truth of the Beast. It was his first-hand, daily experience. But on a Lord's Day, he turned to see a voice that spoke. A voice he'd heard in the Garden, in a boat, by a sea, in a locked room, in a governor's palace, from a cross.
He turned, and saw, and believed once again. And, though he was now old, and the One he loved was ever young, he knew that hope was there, and hope was with him, and one day all things would be made new.
The Critics don't like it, but I think it's a better story. And, as the old quantum scientists knew, sometimes it's the more beautiful story that's the true one.