Deontay Wilder claims he has agreed to fight Anthony Joshua next in the UK, and says it is now up to the Briton's camp to finalise the deal.
WBC champion Wilder took to social media on Monday night to announce to fans that he had agreed to travel to the UK to challenge WBA (Super), WBO and IBF title-holder Joshua to become the undisputed heavyweight champion of the world.
Wilder, who offered Joshua $50m to take the fight in the USA, says that offer is still on the table.
He tweeted: "BREAKING NEWS for all you Anthony Joshua fans... The $50m offer for him to fight me next in the US is still available.
"Today I even agreed to their offer to fight Joshua next in the UK. If he prefers the fight in the UK, the ball is in their court. It's up to them to choose."
Shelly Finkel, Wilder's co-manager, also told ESPN: "We have agreed to the terms that Eddie (Hearn) has put out to us for a fight in the UK.
"Deontay sent an email to Joshua on Sunday night and I sent one today to Barry Hearn and Eddie telling them that we officially accept the offer to fight under the terms they gave us and to send us the contract."
Negotiations have been ongoing since Joshua beat Joseph Parker in March to add the WBO belt to his collection.
It had been thought that the Olympic gold medallist would meet Alexander Povetkin first in September but Wilder has now thrown down the gauntlet.
Jay Deas, Wilder's trainer, told AP that fighting in the UK rather than the US would earn his fighter far less money, but that he was doing it for his "legacy".
"They offered and we accepted. We offered $50m, which is what he said he wanted and then he turned it down", explained Deas.
"Then they came back with a much, much, much smaller offer for Deontay, which would have been even less than Deontay would have made in the United States, and wanted him to still travel to the UK for the fight. And we said yes.
"The reason we did is because Deontay is investing in himself. He wants this for the fans and he wants this for his legacy and he knows that being the undisputed heavyweight champ of the world will give him the financial gain as he proceeds.