In Italy, they are calling it 'the derby of derbies', and with good cause.
On Sunday, AC Milan and Inter will meet at San Siro as the top two sides in Serie A – something which has not happened for 10 years.
Back in April 2011, the Rossoneri had a narrow two-point lead over their city rivals and, despite being shorn of the services of the suspended Zlatan Ibrahimovic, they romped to a 3-0 win on their way to their 18th scudetto – and still their most recent.
But Milan are back. And so, too, is Ibrahimovic, who, at 39 years old, is inspiring the most unexpected of title challenges for a club that was in a state of chaos before his return to San Siro in January of last year.
But while the Swede is defying the ageing process, Stefano Pioli's young squad is beginning to show signs of wear and tear.
The pressure of leading for most of the season appears to be getting to Milan, who gave up first place last weekend because of a worryingly tame 2-0 loss at newly-promoted Spezia. The Rossoneri had reached the New Year undefeated in Serie A; now they have lost three of their past seven games.
The shock setback at Spezia, in which Milan failed to register a single shot on target, allowed Inter to move one point clear with an impressive 3-1 win over Lazio.
Simone Inzaghi's side had won six successive games in Serie A, but they were battered into submission by Romelu Lukaku, who scored two goals and created another.
At times, it felt like Lukaku against the entire Lazio backline – and yet it was not a fair fight.
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In teeing up Lautaro Martinez for Inter's killer third goal, the Belgium international bounded past Marco Parolo in such stunning fashion that it made a mockery of the argument that Lukaku was not fast enough to play the counter-attacking game Ole Gunnar Solskjaer wanted at Manchester United.
As the Gazzetta dello Sport wrote, it was one of those games where Lukaku "looks like an adult playing football with kids in the park". It was a mismatch. But now it is time for a rematch: a battle between two true footballing heavyweights, in every sense of the word.
The Derby della Madonnina is usually bigger than any individual showdown, but Lukaku and Ibrahimovic's bitter row in Inter and Milan's most recent meeting has cast a huge shadow over this weekend's game.
Indeed, it even inspired the creation of a new mural, which adorns a building on Via de Piccolomini, on the south-east corner of San Siro. It shows Lukaku and Ibrahimovic squaring up, and is accompanied by the words, "Face to face, heart to heart."
It is a rather beautiful take on a quite ugly incident.
At the tail end of the first half in last month's Coppa Italia clash between Inter and Milan, Lukaku and Ibrahimovic became embroiled in a war of words after the former had been fouled close to the touchline by Rossoneri defender Alessio Romagnoli.
The row continued on into the penalty area. "Go do your voodoo sh*t, you little donkey,” Ibrahimovc reportedly told Lukaku, making a seemingly very specific reference to comments made by Everton owner Farhad Moshiri about Lukaku and his mother in 2018.
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An enraged Lukaku responded "You want to speak about my mother? F*ck you and your wife!" before offering to continue the discussion in the tunnel: "Well, let's go inside, you b*tch!"
Lukaku had to be held back as the two teams exited the pitch at half-time and ultimately responded in the best possible way.
After Ibrahimovic had been sent off for a second bookable offence, Lukaku levelled the game with a penalty before Christian Eriksen's injury-time free-kick sent Inter through to the semi-finals.
That was not the end of the matter, though. The Italian Football Federation (FIGC) launched an investigation into the Lukaku-Ibrahimovic spat and has yet to make a final ruling. Indeed, Lukaku only gave his side of the story to the FIGC via video call on Monday.
Ibrahimovic, for his part, has rubbished the suggestion that there was a racial element to his comments, stating: “In ZLATAN’s world there is no place for RACISM. We are all the same race – we are all equal!! We are all PLAYERS, some better than others."
That final phrase was construed by some as a dig at Lukaku, whom he has previously mocked over his first touch. There is certainly no denying that the former Manchester United team-mates have developed quite the rivalry since moving to San Siro.
When Lukaku netted in Inter's 4-2 win over Milan last February, he declared, "There's a new king in town." After scoring twice in the next derby in October, Ibrahimovic countered, "Milan never had a king. They have a GOD."
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Both forwards have looked human of late, though. Indeed, before his stunning showing against Lazio, Lukaku had looked a little tired – and with good reason.
No Serie A attacker has played more minutes in all competitions this season than the 27-year-old (2270) – he is that important to Antonio Conte's side.
For all Lautaro's talent and potential, he can be maddeningly frustrating. Lukaku is the far more reliable goalscorer and utterly integral to their attacking game plan.
He is the main reason why Inter are by far and away Serie A's top scorers (55), having been involved in more goals (20) than any other player in the league. Essentially, he is the main reason that they are top.
The Nerazzurri are certainly more reliant on Lukaku than Milan are on Ibra. The Swede's impact, on and off the pitch, at Milan cannot be underestimated, but Pioli has proven that he can mastermind wins without his star striker.
Their surprise title tilt is primarily down to shrewd investment, smart coaching and a united dressing room. This is a team that is very much greater than the sum of their parts.
Ibrahimovic is the obvious leader, of course, and he will be desperate to make a statement after a subdued showing at Spezia by adding to his tally of 10 goals in the derby – particularly now that he has come under fire from the likes of former Milan boss Fabio Capello for agreeing to attend the Sanremo music festival next week.
Lukaku, though, will be looking to become the first player in nearly 50 years to score in four consecutive Serie A fixtures between these two great rivals.
The stage is set, then, for a special afternoon at San Siro. Two heavyweights, one massive rematch. Ibrahimovic and Lukaku are going face to face once again.
It really is the derby of derbies.