Anthony Joshua and Tyson Fury's world heavyweight title showdown has moved a step closer with Joshua's promoter Eddie Hearn saying a two-fight deal has been signed.
The winner of the all-British bout will become the undisputed heavyweight champion.
The locations and dates are yet to be confirmed.
Joshua, 31, holds the WBA, WBO and IBF belts, while Fury, 32, has the WBC title.
All parties have now put pen to paper and we will be working hard over the next few weeks to confirm the site and date for the biggest fight in boxing," Hearn told Sky Sports on Monday.
The fight between Joshua and Fury will see all four belts contested in a heavyweight bout for the first time.
BBC reports the deal is worth NZ$385million - the most lucrative boxing purse ever signed, eclipsing Floyd Mayweather v Manny Pacquiao.
The last undisputed heavyweight champion was Britain's Lennox Lewis from 1999 to 2000, before a boxer had to also hold the WBO belt to be recognised as undisputed champion.
Hearn confirmed the fight purse would be split 50-50 for the first fight, with the winner commanding 60-40 for the second.
A guaranteed rematch clause has been included regardless of the result.