World heavyweight champion boxer Fury, who claimed to have retired after beating Dillian Whyte in April, was in the crowd at the Principality Stadium before becoming involved in the headline clash between Undisputed Universal Champion Roman Reigns and Scottish star Drew McIntyre.
When Austin Theory attempted to capitalise on the brutal contest by cashing in his 'money in the bank' contract on the champion, Fury emerged to floor the 25-year-old with a big right hand.
Fury has been linked with a unification fight against Oleksandr Usyk after the Ukrainian beat Anthony Joshua for the second time last month to retain his WBA (Super), IBF, WBO and IBO heavyweight belts.
Fury posted on social media on Friday to tell Usyk that he will get "smashed to bits" whenever any fight takes place.
But, at a WWE press conference after the event in Cardiff, Fury revealed he would not wait for Usyk.
"I said let's do the fight this year, wherever they want to do it. I've been waiting for countries to come forward," Fury said.
"All of a sudden Oleksandr Usyk has stated he does not want to fight any more - he wants to fight next year not this year.
"I am not going to wait around for anybody and I will be announcing a fight next week."