He was referring to Judas, Simon Iscariot's son, for he was going to betray Him, although he was one of the Twelve.

But Judas Iscariot, one of His disciples, who was going to betray Him, said,

So Jesus, while supper was on -- although He knew that the devil had suggested to Judas Iscariot, Simon's son, to betray Him --

Jesus answered, "It is that one to whom I give the piece of bread when I dip it in the dish." So He dipped it into the dish and took it and gave it to Judas, Simon Iscariot's son.

Judas (not Judas Iscariot) said to Him, "Why is it, Lord, that you are going to make yourself real to us and not to the world?"