Artur Beterbiev and Dmitry Bivol will finally step into the ring opposite each other on Saturday in Saudi Arabia.
Boxing fans have been waiting to see the world light heavyweight champions fight for several years.
All four titles will be up for grabs in Riyadh, with Beterbiev, 39, holding the WBC, WBO and IBF belts, and Bivol, 33, the WBA (Super) champion.
Both men are undefeated and the contest is being touted as a potential classic in the making.
You can follow live text commentary of the main event and undercard, which features two Brits in world title fights, from 19:00 BST on Saturday on the BBC Sport website and app.
Who will be the first undisputed light heavyweight champion in the four-belt era? Who will suffer their first defeat? Could there be a tie in the cards?
BBC Sport has asked for predictions from around the boxing world.
Retired world champion and boxing trainer Anthony Crolla: “You can tell it’s a good fight because a lot of people have a hard time picking a winner, and I’m one of them. If they really push me, I don’t think Bivol has the firepower to do it.” keep Beterbiev away. I see Beterbiev wearing him down and maybe stopping him around the ninth or tenth round.
“But I also wouldn’t be surprised if we see a very disciplined performance from Bivol where he outworks Beterbiev, hits him and moves him, similar to how he did against Saúl ‘Canelo’ Álvarez.”
Skye Nicolson, WBC lightweight champion: “It’s typical fighter vs. boxer, and I have to back the boxer. I find it difficult to see Bivol trapped in a situation he doesn’t want to be in. He’s very good at controlling the distance and pace of the fight.
“But if anyone can do it, it’s Beterbiev. My heart says Bivol.”
Retired world champion Barry Jones: “Beterbiev has to be a slight favorite. He’s knocked out punchers, he’s knocked out boxers and he can knock you out in the first round or the 12th. There’s no round, second or minute where you’re really safe with him.
“But I will continue with Bivol. I have the feeling that his intelligence, patience, discipline and calm attitude could be enough to overcome the dangerous moments and pull him through in a close decision.
“Bivol may have to get up off the ground a couple of times, but I think he could get an early enough lead to sneak home.”
British heavyweight champion Fabio Wardley: “I’m getting close to Bivol, but this is probably one of the hardest fights to predict in boxing right now. It’s a real fight with two men with completely different styles. Beterbiev is a destroyer who can clean up everyone. Bivol has great power but he is a very clean and precise boxer.
“It’s a question of who can best impose their style on that night and make an impact.”
Heavyweight Frazer Clarke: “I keep changing my mind. I’ve been saying Beterbiev all along, but now I think Bivol could handle this one. It’s a 50/50 world class though.”
Retired world champion Darren Barker: “I would have Beterbiev as a favorite. When you have that power, he knocks people down with punches. How can you not have him as a favorite? He’s not huge, but at any moment he could turn off Bivol’s lights. But I’m going to use Bivol.” “A unanimous decision but a very close fight. What I mean by that is that the rounds will be enough. I’m going to go with the matador in this fight, but I wouldn’t put my house on it.”
Bivol promoter Eddie Hearn: “When you fight Beterbiev, it’s like a time bomb. The speed of that time bomb depends on the opponent. Dmitry has the ability to make it work very slowly. How slow can he make it? The peak point is 12 rounds .
“Beterbiev is going to catch you, but how fast can he catch you and how much time do you have left until he catches you? The only person who can beat Beterbiev right now is Bivol.”
Former world champion Hannah Rankin: “This is a brilliant matchup between two fighters who have been waiting to fight for a long time and now all the marbles are on the line.
“I’ll take Bivol in the points, as he’s the younger and fresher of the two, with less wear and tear on his body. However, I wouldn’t be surprised if Beterbiev drops Bivol during the fight.”
Saudi welterweight Ziyad ‘Zizo’ Almaayouf: “Call me crazy, but I think Bivol takes it too quickly. There will always be danger from Beterbiev, but I see that Bivol controls the distance too well.”
Former world champion Regis Prograis: “I have to bet on Bivol, he’s a beast. It’s a really good fight, the only bad thing is that they don’t have big names for those who aren’t boxing fans. But it’s an amazing fight.”
Retired world title challenger Paul Smith: “From the beginning I have said Beterbiev and I think it could be a late stoppage. I don’t think there is anyone who can keep him away. He is too relentless.
“Bivol is obviously exceptionally good and has incredible footwork, so I wouldn’t be surprised if he won. But I’ve always felt that Bivol, other than against Saúl ‘Canelo’ Álvarez, has done enough to win fights and I’m not sure. that’s enough against Beterbiev. I don’t think he hits hard enough to earn Beterbiev’s respect.”
English Cruiserweight Champion Viddal Riley: “I’ll take Bivol. He has better movement, better fluidity and will be able to outplay Beterbiev in most rounds. But as we get to the later rounds, it will become a war.”