TSK · John 19:26

One of his disciples, whom Jesus loved, was at the table, leaning against Jesus' breast.

That disciple therefore whom Jesus loved said to Peter, "It's the Lord!" So when Simon Peter heard that it was the Lord, he wrapped his coat around him (for he was naked), and threw himself into the sea.

This is the disciple who testifies about these things, and wrote these things. We know that his witness is true.