The Champions League waited 58 years for a derby in a final.
Now it has a second in three seasons, both involving the same two sides. Madrid's position as Europe's unofficial footballing capital has been underlined.
Either Real will win a record 11th European Cup or Atletico a long-awaited first. Either Zinedine Zidane's first half-season in major management will be a remarkable success or Diego Simeone will manage to overturn the financial gulf to make Atletico's relative paupers Europe's top team.
They have already eliminated the two many considered its best. After knocking out Barcelona and Bayern Munich, they have established a right to be champions.
And they nearly did that too, in a committed final display two years ago, before Sergio Ramos' 93rd-minute equaliser took the game into extra-time, when Real won 4-1 and the temperamental Simeone imploded.
A reunion provides a contrast between clubs, the entitled aristocrats against the scrappy underdogs, and a clash of styles.
Atletico averaged 26.1 percent of possession against Bayern and Barcelona. They have Europe's best defence, Real its most potent attack.
Consider the statistics from La Liga: Real scored 110 goals and Atletico a mere 63, but only two points separated them. That was because Atletico conceded just 18 times.
They will defend deep and in numbers. In Diego Godin, their 2014 final scorer, they may have the finest centre-back in the world. Jan Oblak is a worthy successor to Thibaut Courtois in goal.
Simeone has constructed a team that is greater than the sum of its parts, one which can swop between the favoured 4-4-2 and 4-3-3, but which is notable for its coherence, its ferocious intensity and its counter-attacking prowess when they regain the ball.
Real have a more individualistic culture. They do not just chase Galacticos; they indulge them.
But Zidane, beaten only twice in his 26 games in charge, has managed to do something his predecessor Rafa Benitez could not, by convincing president Florentino Perez that he needs the unflashy defensive midfielder Casemiro.
He will be charged with providing the platform for Real's playmakers, Toni Kroos and Luka Modric, to supply the flying wingers Gareth Bale and Cristiano Ronaldo.
The Portuguese is a phenomenon. He has a record 93 Champions League goals, in addition to the fact that he is set to finish as its top scorer for a fourth consecutive year.
And yet while he is a goal machine, Real have only struck twice in their last five games against Atletico, neither from Ronaldo. The rejuvenated Fernando Torres and the remarkable Antoine Griezmann both have more goals in the last six derbies.
So as opposites and enemies meet, it is a question of whether Atletico can bridge the gap in ability and if they can shrug off their historic inferiority to inflict Real's most painful ever European defeat and gain revenge for 2014.
ATLETICO MADRID V REAL MADRID
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