Jesus says the temple will be destroyed.
Disciples asks when?
Jesus launches into his apocalyptic prophecy including the following...
False messiahs, wars, famines, earthquakes, persecution, many leave the faith, false prophets deceive many, love of most grows cold, gospel preacehd throughout the earth, Jerusalem under seige, signs in sun moon and stars, sign of son of man in heaven with power and great glory, gathering of the elect from the four winds.
Then he addresses the question of when?
The answer is that he doesn't know BUT - " Truly I tell you, this generation will certainly not pass away until all these things have happened."
His followers organised their lives accordingly. He was a false prophet.