Negotiations to pit Anthony Joshua against Tyson Fury are "moving forwards" with both sides aiming for a 2021 summer showdown, says promoter Eddie Hearn.
Joshua and Fury, who hold every heavyweight championship between them, have agreed the finances to stage two undisputed title fights next year and their representatives are now discussing finer details.
"The bulk is done, the financial elements of the deal," Hearn told Sky Sports.
"There is always stuff that is out of our control, ie the fighters winning their next fights.
"[Fury's US promoter Bob Arum and I] had a good chat [on Thursday]. We're getting along alright. We have our words backwards and forwards but we both want to make the biggest fight of all time.
"He's made many of them in the past and I want to make one that goes down in history as well.
"We're all moving forwards. We talked about the site, the other elements of the deal and we agreed to move forwards by papering this. Dotting the i's and crossing the t's. Get this boxed in for 2021."
Fury's UK promoter Frank Warren previously told Sky Sports: "All that's agreed is a 50-50 split. There is a mountain of stuff, and I'm not wanting it not to happen.
"The way forward is to get everybody to get together, get everyone around the table and sort it out, and that's how it will be done.
"Who walks first? What side of the poster? Just toss a coin. Let's make a list, here's the 10 points. Spin a coin, whoever wins, you've got the first one, he's got the second one. Get it on. Stop putting obstacles in the way. There are no obstacles in the way of this fight."
Joshua will next defend his IBF, WBA and WBO titles against Kubrat Pulev while Fury will meet Deontay Wilder in a third WBC title fight.
Asked when Joshua and Fury could realistically share the ring, Hearn said: "Next summer. I think there will be two next year.
"Everybody knows, including AJ and Fury, we would love this to take place in the UK. It's two Brits fighting for the undisputed championship.
"But there is so much interest from around the world that I do believe one of these fights will take place outside of the UK.
"I'm happy to do one in the UK, one outside. But I'd be disappointed if we couldn't do one in the UK.
"The fighters and their close teams will make a collective decision.
"While I want it in the UK, I just want the fight. I want to see AJ become undisputed heavyweight champion of the world."
Dillian Whyte will defend the interim WBC belt and his status as Fury's mandatory challenger in a heavyweight clash with Alexander Povetkin that concludes Fight Camp on August 22, live on Sky Sports Box Office.
Whyte has been the WBC's No 1 ranked contender for a lengthy spell of over 950 days, but is still awaiting a first world title opportunity.
"Once a promise has been made, it was February 2020 then it was delayed by a year, then enough is enough," Hearn said.
"Whyte should take priority over Joshua to get the Fury fight.
"Joshua will fight Pulev in November so won't fight until May, June or July of next year anyway. So there's no reason why Whyte shouldn't get that shot."