Throughout His ministry on the earth, Jesus chose to reveal who He really was only to a select few people. He hid the truth to the public, speaking in parables so that “Seeing they may not see, and hearing they may not understand” (Luke 8:10). He silenced demons who identified Him as the Son of God, and He did not refer to Himself as the Messiah except in indirect ways (as in Matthew 11:2-6). The truth was not revealed until He was crucified:

John 19:19-20
19 Pilate also wrote an inscription and put it on the cross. It read, “Jesus of Nazareth, the King of the Jews.” 20 Many of the Jews read this inscription, for the place where Jesus was crucified was near the city, and it was written in Aramaic, in Latin, and in Greek.

The moment when Jesus was finally announced as the King of the Jews — the descendant of David who was to rule Israel as its Messiah — was the time of His greatest suffering and shame. How painfully ironic it must have been to His followers to see the truth finally revealed, plain as day, broadcast in many languages to all who passed by…but its Author mocked and crucified. They didn’t realize how important it was for Jesus to reveal Himself as the Suffering Servant from Isaiah — that He had come to bleed and die for the sin of the world. His suffering did not disqualify Him from kingship; rather, it was the mark of His kingship and reign over all the earth.

UPDATE July 3: It just occurred to me that I totally forgot about the Triumphal Entry, where people were calling out, “Blessed is he who comes in the name of the Lord, even the King of Israel!” (John 12:13). So despite what I said above, Jesus was announced as King and Messiah before the cross. However, the inscription on the cross still shows the link between His suffering and His kingship.