Hezekiah's sons?

Today I was reading Zephaniah and some commentary on it.
The first verse got me asking a question:
1The word of the LORD which came unto Zephaniah the son of Cushi, the son of Gedaliah, the son of Amariah, the son of Hezekiah, in the days of Josiah the son of Amon, king of Judah.

I think that both Zephaniah and Josiah are related.
Zephaniah is the son of Cushi, who is the son of Gedaliah, who is the son of Amariah, who is the son of Hezekiah.
And Joshia is the son of Amon, who is the son of Mannaseh, who is the son of Hezekiah.

Mt. 1:10: Hezekiah the father of Manasseh, Manasseh the father of Amon, Amon the father of Josiah

So basically Zephaniah and Josiah were cousins!