The whelp, as Ezekiel 19:4 shows, is Jehoahaz, also known as Shallum (Jeremiah 22:11), who "did evil" in the sight of the Lord (2 Kings 23:32), the words that follow pointing to cruelty and oppression like that of Zedekiah.
The passage finds a somewhat striking parallel in AEschylus, 'Agam.,' 695-715.