Both clubs come from the same Italian city, both share the same iconic stadium but only one will qualify for the final of the Champions League.
AC Milan and Inter Milan are set to face each other in the semifinal of Europe's most prestigious competition and the stakes couldn't be much higher.
Wednesday's first leg promises to bring the city of Milan to a standstill, with both fan bases being some of the most passionate supporters in European soccer.
Those who don't manage to get tickets to watch inside the San Siro stadium will be meeting in bars and cafes, praying it's their team that comes out on top.
As testament to the strong feelings in the city, one 100-year-old fan said he would be willing to give up his pension for an Internazionale win.
"I prayed to God to give me the joy of Inter winning, and hopefully He will agree," Enrico Vanzini told Reuters.
"I would do anything (for a win), including (giving up) my small pension," Vanzini continued, saying he would watch the first leg from his nursing home in Padua, Italy.
Meanwhile, Italian soccer journalist Tancredi Palmeri told CNN Sport that there would be no "winners" of the tie, only "survivors."
If that's true, the survivor will not only get one over on its bitter rival but will also have the chance to add yet another European title to its trophy cabinet.
With seven titles already to its name, AC Milan knows how to win in this competition -- only Real Madrid has won more with 14 -- but last lifted the trophy in 2007, coincidentally with current Madrid manager Carlo Ancelotti holding the reins.
Meanwhile, Inter has won three titles with its last successful campaign coming back in 2010 when Jose Mourinho's men beat Bayern Munich in Madrid.
While the two teams regularly compete in domestic competitions every year, it's the first time in 20 years that two of the world's most recognizable clubs will play each other in the semifinals of the Champions League.
AC Milan got the better of the 2003 encounter before going on to beat Juventus in the final.
Since then, both clubs have been through somewhat of a transition period and no longer have the financial power to compete with some of the biggest names in European soccer.
As a result, both have somewhat overachieved in reaching the final four of the competition and the winner will face a difficult test against either Manchester City or Real Madrid in the final.
Inter probably has the edge over AC Milan given recent history, with Simone Inzaghi's side winning the last two meetings this year -- including a 3-0 victory in the Italian Supercup.
"We will have to be very good at using our heads when we need to because there are always unexpected events in such important matches: in the last ones, we have always been good at being lucid," Inzaghi told reporters Tuesday.
"It's a very important match as other finals have been. It's not a derby, but the derby. We know what it means for us, for the club, for the fans, even for myself. But I'm quite serene, I've seen the boys very focused."
Centenarian Vanzini had one more bit of advice for Inzaghi and the Nerazzurri ahead of the match: "In the first half, we must not get too tired, everyone must be in their place."
AC Milan, which was replaced as Serie A champion by Napoli last week, has also struggled for form in the league and has slipped to fifth after winning just three of its last 10 matches.
But manager Stefano Pioli says the team is focused on upsetting the odds one more time.
"We are talking about Champions League, we have not had ups and downs but an outstanding run," Pioli told reporters Tuesday.
"We want to try to overcome this last step before winning a Champions League final, something that hasn't happened to all of us. Motivation is at its highest.
"It is the most difficult because it is a Champions semifinal. But it is also beautiful to prepare, to experience, to play. I have tried to transmit concentration and happiness to the team to live these moments."
The first leg kicks off on Wednesday with the return leg scheduled for May 16.
