Luke 9. My Son

Luke 9:35 NIV
A voice came from the cloud, saying, “This is my Son, whom I have chosen; listen to him.”

This happen when Jesus transfigure at the mountain.

The earlier when God proclaim Jesus As His Son was after Jesus being Baptist.

Luke 3:22 NIV
and the Holy Spirit descended on him in bodily form like a dove. And a voice came from heaven: “You are my Son, whom I love; with you I am well pleased.”

Notice God not letting Jesus, His Son,  alone,  at least until now,  He had acknowledge Jesus twice as His Son. Also in later He is promoting His Son.

Luke 9:28 NIV
About eight days after Jesus said this, he took Peter, John and James with him and went up onto a mountain to pray.

Peter,  John and James, were with Jesus.

Peter,  appear many times in bible and also in the Book of Act.

James,  wrote the Book of James.

John,  if not taken he wrote the revelation.
Jesus said this when He first talk about His death.

Luke 9:27 NIV
“Truly I tell you, some who are standing here will not taste death before they see the kingdom of God.”

Is this refer to John?  Did John die after he finish the revelation?