John 13:20

‘When Jesus had spoken thus he was troubled in spirit and testified saying, “I emphatically inform you that one of you will betray me”.'

Jesus now confirms that he knew at this point that Judas had made his final decision. That he had hardened his heart and was now beyond helping. But this was not something that was easy for Jesus to accept. He had clearly loved Judas and felt deeply betrayed. Thus His spirit was troubled within Him, and this forced out of Him the anguished words ‘one of you will betray me'. The plain truth could be held back no longer.

Betrayals, however, are of many different kinds, and there would not have dawned on the disciples either the nature of the betrayal, the closeness timewise of its occurrence, nor its dark consequences. They did not know what we know. Indeed we learn from the other Gospels that each thought that it might be him. They were thinking in terms of a slip up (like that of Peter later) rather than of a catastrophe.