Anthony Joshua will fight Alexander Povetkin at Wembley in September, promoter Eddie Hearn confirmed on Monday.
IBF, IBO, WBA and WBO champion Joshua and Hearn had earlier announced dates for two fights at the national stadium in London, with bouts on September 22 this year and April 13, 2019.
And Povetkin, as expected, will provide the Briton's first opponent.
Povetkin (34-1) stated: "The battle for the world title has always been my goal. I fought for the moment to face the strongest in the world and, on September 22, I get my opportunity.
"Anthony Joshua has four belts and I want them all. I'm glad that our fight will finally take place, the meeting of two Olympic champions in the ring is destined to be a breathtaking event."
Joshua had been ordered by the WBA to take the mandatory fight to defend his belt, as negotiations faltered with Deontay Wilder over a potential unification bout. Wilder remains a possible opponent for April after Hearn confirmed last week that Joshua is ready to sign a contract.
Former world champion and Sky Sports pundit Johnny Nelson views Povetkin as a very serious challenge.
"This is a serious, serious threat for Anthony Joshua. Everybody has been talking about the big fight between AJ and Deontay Wilder, but are they forgetting about Alexander Povetkin? I think they might be. I think they have forgotten about his pedigree, they've forgotten about what he is capable of doing in the ring. Well, I have seen it so many times in this sport when fighters are already looking at their next fight, and I hope Joshua isn't doing the same," Nelson told Sky Sports.
"Povetkin can fight. This is going to be a tough one and it could well be the toughest test of the lot. You could argue that Wladimir Klitschko was past his best, or that Carlos Takam was a short-notice opponent, or that Joseph Parker has a granite chin, but the one thing we know Povetkin can do, is fight.
"He doesn't just have power, he has pace, and he will use the fact he will be much shorter to walk in low and put pressure on. He is not going to throw thousands of punches, but he's consistent and he was a world champion between 2011-2013. A big thing Povetkin has is experience. Looking good against someone like him is one thing, but quite simply, Povetkin definitely has the capabilities of beating 'AJ'.