Matthew 16:28 Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.
Matthew 17:1-3 And after six days Jesus taketh Peter, James, and John his brother, and bringeth them up into an high mountain apart, And was transfigured before them: and his face did shine as the sun, and his raiment was white as the light. And, behold, there appeared unto them Moses and Elias talking with him.
Peter wrote about what he and James and John had witnessed that day on the mountain in 65AD, 5 years prior to what you call the return of Christ.
He told us, that he had already witnessed this event.
2 Peter 1:16-18 For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty. For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased. And this voice which came from heaven we heard, when we were with him in the holy mount.
Jesus told His disciples that some there would see Him coming in His glory.
Six days later, Peter James and John did.
Jesus told them not to tell anyone about it until after His resurrection.
Around 30 years later, Peter recorded what they had seen, right down to the voice of the Father saying "This is my beloved Son in whom I am well pleased."
How much longer can you complicate this?
JH :-)