Wilder emailed Joshua promoter Eddie Hearn of Matchroom Boxing an offer of a minimum of $50 million for Joshua to fight him for the undisputed heavyweight championship in their next bout -- before the end of this year -- both sides told ESPN.

Shelly Finkel, who manages Wilder along with Al Haymon and trainer Jay Deas, said the offer is for $50 million against 50 percent of the event revenue, meaning Joshua would make no less than that figure no matter how much the fight generated. If the fight generated more than $100 million, which Finkel believes it could, Joshua would make even more, and if it lost money, the Wilder side would be on the hook to pay Joshua.

"It's a giant number," Finkel said. "But it's also a giant fight."

Finkel detailed additional elements of the offer for what would be a pay-per-view fight in the United States; all of Joshua's title fights have been on pay-per-view in the United Kingdom, his home country. Finkel said the offer calls for the Wilder side to select the location of the fight, but they would look to do it in the United States, probably Las Vegas.

He also said there would be no rematch clause and the fight would have to be next for each man. As for the timing of the bout, Finkel said it would take place between September and the end of the year.

"It has to be the next fight for each of them," he said. "No rematch clause, and it's for all the belts. We asked for them to send us an acceptance [by the end of Thursday]. Joshua [previously] asked for $50 million against 50 percent, and we gave it to them. They probably don't believe it's this big of an offer, but it's an unbelievable offer. I hope they accept. Deontay is thrilled and believes Joshua will take it."

The offer was made as a counter-offer to the one Hearn put forth in recent weeks, which called for Wilder to be paid a flat $12.5 million fee with no percentage of the event, a nonstarter for a fight of this magnitude -- by far the biggest in the heavyweight division and one of the biggest in boxing.

Wilder, who has been calling out Joshua for more than a year to meet him to unify titles, made a video directed at Joshua that he posted on social media on Wednesday.

"Anthony, get your man Eddie and [his father] Barry Hearn to check their email. I got something special for you," Wilder said. "By the way, all the money's in the bag. So I expect you'll be a man of your word."

At that point, Wilder's video cut to video of an interview Joshua gave earlier this month to Sky Sports, the broadcast outlet he has a deal with in the U.K., in which he said of a possible Wilder fight, "I'll take $50 million up front. If that's the case, Wilder's team, bring me $50 million up front, and we'll take the fight."

Wilder concluded his 30-second video by saying "I'll see you soon then" as he salutes.

Hearn told ESPN that he had indeed received the offer by email from Wilder's personal account, and Wilder noted Joshua's request in the Sky interview for $50 million against 50 percent of the event.

"To me, this look like a PR move, but it's something we obviously take seriously," Hearn said. "I'll be asking for a contact and also some answers to some important questions, like where is the fight going to be?"

Joshua and Hearn thought any deal would be for two fights, with an automatic rematch.

"There's no second fight in the offer. That's not the end of the world if the deal is right," Hearn said. "There are obviously other things that need to be addressed. Joshua has a number of existing broadcast deals in multiple territories [though he is a free agent in the U.S.]. Also the offer comes from Deontay Wilder and, with all due respect, he doesn't have $50 million, so we need to know where the money is coming from. We want to do the fight in the U.K., but if we get an acceptable and secure offer, we'll certainly look at it and take it seriously."

Hearn is in New York this week because he is promoting an HBO doubleheader at Barclays Center in Brooklyn headlined by Daniel Jacobs against Maciej Sulecki in a middleweight world title eliminator. While he is here, he, Finkel and Haymon are scheduled to meet Friday to discuss a Joshua-Wilder deal.

"They said we have to accept the fight by [Thursday], which is ridiculous when we have questions that need to be answered," Hearn said. "But we have a meeting on Friday, and we will go through the offer. I'd like to see a contract and see where the money is coming from, and the location of the fight is important. We don't have a problem doing it in America, even though we'd like to do it in the U.K."

The 28-year-old Joshua (21-0, 20 KOs) won a world title in 2016 and has made five defenses, including unifying three belts with a decision win against Joseph Parker on March 31 in Cardiff, Wales. Wilder (40-0, 39 KOs), 32, of Tuscaloosa, Alabama, won his belt in 2015 and has made seven title defenses, including scoring a massive 10th-round knockout of then-unbeaten top contender Luis "King Kong" Ortiz in a riveting fight on March 3 at Barclays Center.