Seeing the kingdom of God

Jesus made an astounding prediction.

But I tell you truly, there are some standing here who will not taste death until they see the kingdom of God.
Luke 9:27

Aside from Jesus himself everyone who was there is now dead, so this prophecy must have been fulfilled.  But just when did its fulfillment take place?  The prophecy appears in three gospels, Matthew, Mark, and Luke, and in all three is immediately followed by the event known as the Transfiguration.

Now about eight days after these sayings he took with him Peter and John and James and went up on the mountain to pray. And as he was praying, the appearance of his face was altered, and his clothing became dazzling white. And behold, two men were talking with him, Moses and Elijah, who appeared in glory and spoke of his departure, which he was about to accomplish at Jerusalem.

Now Peter and those who were with him were heavy with sleep, but when they became fully awake they saw his glory and the two men who stood with him. And as the men were parting from him, Peter said to Jesus, “Master, it is good that we are here. Let us make three tents, one for you and one for Moses and one for Elijah”—not knowing what he said.

As he was saying these things, a cloud came and overshadowed them, and they were afraid as they entered the cloud. And a voice came out of the cloud, saying, “This is my Son, my Chosen One; listen to him!” And when the voice had spoken, Jesus was found alone. And they kept silent and told no one in those days anything of what they had seen.
Luke 9:28-36