KSI was beaten as a boxer for the first time after six scrappy rounds at Manchester’s AO Arena.
He came out on the wrong end of a majority-decision despite Fury having a point taken for punches to the back of the head.
Still his aggression and work rate saw him scrape a win – leaving KSI in rage at the result.
He said: “We’re gonna appeal. I want to appeal. I’m sorry that is outrageous.”
In a separate rant, KSI fumed to Fury: “Robbery, it’s a robbery. You weren’t landing, look at your face.
“Look at you. I’m the YouTuber and you’re the boxer, you have to win.”
Fury, 24, came into the Battle of Britain bout having beaten KSI’s arch rival Paul, 26, over eight rounds in February.
The American was ringside to watch his old rivals do battle having cornered brother Logan, 28, to victory over Dillon Danis, 30.
And he was quick to rub salt in the wounds after watching KSI suffer the same fait as him against Fury.
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Paul posted on X, formerly Twitter: “HAHAHAHA KSI SORE LOSER CHOKING UP.
“Only thing that got robbed is his hair line It’s okay KSI me too it’s gonna be okay bubba.
“I took my loss like a man from the scorecard read and showed the youth how to learn from it and come back to take a W.
“This 30 year old man crying for an appeal.”