This was the promise that God gave to David.

Psalms 89:3-4 says,

"You said, "I have made a covenant with my chosen one, I have sworn to David my servant, 'I will establish your line forever and make your throne firm through all generations.'"

That throne was to stand forever as attested in verses 28-37,

"Once for all, I have sworn by my holiness and I will not lie to David—that his line will continue forever and his throne endure before me like the sun; it will be established forever like the moon, the faithful witness in the sky."

Jeremiah 33:17 (KJV) says,

"For thus saith the Lord; David shall never want a man to sit upon the throne of the house of Israel"

Zedekiah was the last king to sit upon the throne of the Jewish nation of Judah. He was descended from the royal line of David of the Pharez branch of the tribe of Judah, and all of his sons were captured and taken from Jerusalem to Babylon, where his sons were slain in front of Zedekiah’s eyes and then he was blinded, so that the execution of his sons would be the last thing he ever saw. This all occurred years before Jesus was born.

My Question to you is, did God not fulfill his promise that a man would reign on David’s throne forever?