Dillian Whyte has signed a contract to fight WBC heavyweight champion, Tyson Fury, just hours before the deadline.
The fight is expected to take place on 23 April, potentially at Wembley Stadium.
Whyte, 33, had until 06:00 GMT on Tuesday to sign but had spent the weekend and Monday negotiating details of the deal.
"Dillian Whyte signed his contract for $8m, what a surprise," Fury said on social media.
Fury added: "An absolute idiot. Should this even be a talking point? The man's signed for the biggest payday he's going to get in his life."
Whyte is the mandatory challenger to Fury's WBC belt and has been waiting years for a shot at the world title as the WBC's number-one-ranked contender.
After lengthy discussions between both teams came to nothing, Frank Warren's Queensberry Promotions won the purse bids in January with a $41m (£30m) bid, beating Whyte's promoter Eddie Hearn who was the only other bidder.
Fury, 33, is now set to receive 80%, around £20m, of the purse and Whyte the remaining 20%.
Whyte has been pushing for a bigger split of the purse bid but the £5.6m he is guaranteed to receive will be the biggest payday of his career to date. There is also a further £3.1m on offer for the winner.
Fury has not fought in the UK since August 2018 when he beat Francesco Pianeta having fought exclusively in the US since signing a promotional deal with Bob Arum's Top Rank.
Whyte has built a formidable reputation in UK with just two defeats on his record. There was a suggestion his decision to delay signing his contract was an attempt to unsettle Fury, but the 'Gypsy King' poked fun at the idea.
He joked: "My head hurts from all the mind games Dillian Whyte has been playing on me. Oh my god. I'm so sore I don't know whether I'm coming or going, my training's camp a mess."
Fury, who is unbeaten in his pro career with 31 wins and one draw, will now need to seek a boxing licence from the British Boxing Board of Control.
A news conference officially announcing the fight could happen as early as Wednesday. Cardiff's Principality Stadium is still an option to host the bout although the 90,000-seater Wembley Stadium, a venue neither fighter has headlined, is a clear favourite.
There is still one final outstanding issue between Fury and Whyte to be resolved before an official announcement is made.
