It was a clear shot at Morgan, who recently called O'Reilly a "complete dick" over an awkward encounter between the two at a New York Knicks game.
Morgan wasted little time to respond, using his Twitter account call O'Reilly a "flaming hypocrite" and declare Megyn Kelly the "new star" at Fox News.
Got to laugh at @oreillyfactor accusing ME of personal attacks. Guy's made a career out of it. Get over yourself, you flaming hypocrite.— Piers Morgan (@piersmorgan) November 21, 2013