What follows is the word that Yahweh gave to Zephaniah during the reign of King Josiah of Judah (640-609 B.C.). This "word"includes all that the Lord told the prophet that He also led him to record for posterity (cf. Hos. 1:1; Joel 1:1; Mic. 1:1). This was a divine revelation that God gave through one of His servants the prophets.
Zephaniah recorded his genealogy, the longest genealogy of a writing prophet in any prophetical book. It goes back four generations to Zephaniah's great-great-grandfather, Hezekiah. As noted in the "Writer"section of the Introduction above, it is impossible to prove or to disprove that this Hezekiah was the king of Judah by that name. Chronologically he could have been since people married quite young during Israel's monarchy. I think this Hezekiah probably was the king since the name was not common and since it would make sense to trace the prophet's lineage back so far if Hezekiah was an important person (cf. Zech. 1:1). Normally the writing prophets who recorded their ancestors named only their fathers (cf. Jon. 1:1; Joel 1:1). We have no complete genealogy of King Hezekiah's descendants in the Old Testament.