Commonwealth light-heavyweight champion Tony Bellew has stepped in to fight Nathan Cleverly for the WBO light-heavyweight title on Saturday.
Welshman Cleverly was left without an opponent after WBO belt-holder Juergen Braehmer pulled out on Wednesday, claiming to have an eye injury.
Cleverly will fight as champion at London's O2 Arena after the WBO stripped Braehmer of his belt.
"I'm really happy that Bellew will be in the opposite corner," he said.
"I knew we'd get it on one day and that day has come sooner than expected. I'm ready - he's going to get knocked out."
Bellew, who was in training for a rematch against Ovill McKenzie, said: "I'm coming down to London to fight and believe [me] when I say I'm going to knock Cleverly out cold."
The 28-year-old has won all 15 of his professional fights, with 10 of those victories coming via knock-outs.
"I wouldn't have put myself forward if I didn't think I could beat him," he said. "Two months notice or two day's notice, I know I can beat Cleverly."
Cleverly, 24, added: "Not only will Bellew feel my anger from Braehmer pulling out, but he'll now pay for slagging me off in the last year."
Promoter Frank Warren said: "The fight between Nathan and Tony has been brewing up in the last year and it's happened sooner than expected, but I'm delighted that it's on.
"There is nothing like big domestic fights - I'm expecting fireworks in the ring."
Warren was furious after Braehmer left him in the lurch on Wednesday, calling for the German to be stripped of his title and Cleverly to be declared WBO champion.
The German failed to turn up in London and did not even inform Warren's team of his withdrawal.
The WBO's European chairman Istvan Kovac confirmed his title had been awarded to Cleverly.
"This is the third time Braehmer has pulled out of a title defence at short notice," he told Reuters.
"He has had some personal problems in the past and I hope he can come back and fight again.
"But Nathan Cleverly is now the world champion and rightfully so because none of this was his fault."
Warren labelled Braehmer's pull-out as "the most unprofessional" he had experienced in 30 years of promoting and added that the manner of the postponement was "disgraceful".
Braehmer's stock is already low because the 32-year-old has only defended his belt once since winning it in 2009, also pulling out of a January unification fight with Beibut Shumenov.
The German last fought in April 2010 and has 29 knockouts from 36 wins with two defeats.
Since that last fight Braehmer was involved in a long-running court case that could have resulted in him being jailed for 16 months for assault and insulting behaviour.
Braehmer was cleared this year following an appeal, meaning the German kept his WBO title.
But this latest incident will likely lead to the German losing his world title status.
Cleverly became the interim champion in December following a far from impressive points victory over Nadjib Mohammedi.
His fight with Bellew tops a bill which also includes James DeGale's grudge fight against George Groves for the British and Commonwealth super-middleweight titles.
"Cleverly is a great fighter but that's going to be a tough first defence," added Kovac, the Hungarian former Olympic champion.
"Braehmer is a southpaw and all Cleverly's sparring has been against southpaws whereas I believe Bellew is orthodox. It will be a real title defence."