One of the fiercest rivalries in world football could be reignited on Friday when Jose Mourinho learns who his Chelsea side will face in the semifinals of the Champions League.
he Blues once again defied the odds to progress in Europe's top club competition on Tuesday, beating Paris Saint-Germain on away goals thanks to Demba Ba's late strike at Stamford Bridge.
On Wednesday, Pep Guardiola's Bayern Munich booked their place in the last four by beating Manchester United 3-1 to prevail 4-2 on aggregate.
There could be fireworks should Mourinho and Guardiola be pitted against each other when the draw is made in Nyon at 11:00 GMT.
When Sir Bobby Robson was in charge of Barcelona in the 1990s, Guardiola was his midfield maestro while Mourinho's role was assistant to the former England boss.
However, when Mourinho became Real Madrid coach, the pair became increasingly bitter enemies.
Guardiola, normally such a calm and controlled person, used a series of expletives when talking about Mourinho and his conduct in news conferences, while on the pitch, Barca and Real fought an increasingly bitter war.
Mourinho is reluctant to speak about Guardiola, and at last year's Super Cup, the Portuguese snapped at one reporter who pointed out that he had only won three of his 15 meetings with the Spaniard. That became three in 16 when Bayern defeated Chelsea on penalties in Prague.
But Guardiola, it seems, is a little bit more willing to build bridges.
He showered praise on all three potential Champions League opponents following the 3-1 win over United, but Mourinho was the only coach he mentioned when giving his assessment of the draw.
“Chelsea have a manager with a lot of experience,'' Guardiola said. “They are an English team with many qualities and experienced players like Petr Cech, Branislav Ivanovic, John Terry and Frank Lampard.''
There is a lot at stake for Mourinho. He is bidding to become the first man to win the European Cup with three different teams.
A match-up against Real Madrid would also be intriguing for the Portuguese. Mourinho left the Bernabeu in acrimonious circumstances last summer after winning the league just once in his three-year spell in charge.
The 51-year-old is not desperate to face his old team, though, who will be without Cristiano Ronaldo for the first leg because of a thigh injury.
“No, not really,'' was Mourinho's answer when asked whether he would be hoping for Luis Figo to draw Chelsea against Real Madrid on Friday. “It doesn't matter who we face.''
Real Madrid have fallen behind surprise leaders Atletico Madrid in the Primera Division and Diego Simeone's side are making a strong push for European glory as well.
Atletico beat Barcelona to qualify for the semifinals of the European Cup for the first time in 40 years this week, and they did so without the injured Chelsea target Diego Costa.
Mourinho won eight of nine Madrid derbies during his time at the Bernabeu, but Atletico are now a far more formidable force under Simeone.
If Chelsea draw Bayern, then Atletico and Real would meet for the first time in Europe since 1959.
The first legs of the semifinals will take place on April 22 or 23, with the return legs taking place a week later.
The Europa League semifinal line-up will also be decided just before the Champions League draw is made.