Around two decades ago, Jurgen Klopp faced Ralf Rangnick while in charge of Mainz 05. The two coaches weren't personal friends at the time but their coaching styles appeared to be similar.
Shortly after the contest, the latter called the former to ask him questions about one of his upcoming opponents.
The team in question had faced Klopp's Mainz outfit just days earlier and Rangnick was keen to pick his brain for information.
The duo have shared a distant relationship since.
But this weekend Rangnick could once again rely upon Klopp to shape his tactics - and he could do Liverpool a favour in the process.
Manchester United travel to Manchester City on Sunday afternoon.
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City are incredibly difficult to beat but Klopp has proved to be more successful than most of his peers when it comes to inflicting damage upon their manager.
Of all the coaches who Pep Guardiola has faced more than six times in his career, his record against the current Liverpool boss is his worst.
He averages just 1.41 points-per-game against Klopp.
No wonder, then, that Rangnick, currently in caretaker charge of United, could once again seek assistance from his compatriot Klopp.
But rather than calling him and conversing over the phone as he did in Germany all those years ago, he could use his colleague's tactical blueprint from previous meetings as a template from which to work.
When facing City - especially away from home - Klopp tends to instruct his players to refrain from pressing high up the field.
Instead, Liverpool typically focus on blocking the centre of the park. "What does City want to do? They want to play through the centre," said Klopp after facing Guardiola's team at Anfield in October.
As a result, Guardiola's players are usually presented with two options, as shown below. They can either build using the flanks, which allows their opponents to remain relatively safe, or they can take risks by forcing passes through the middle.
The latter can sometimes allow Liverpool to counter-attack. Klopp's side have focused on intercepting those passes in previous meetings before launching quick moves towards goal. United have the make-up to behave in a similar manner on Sunday afternoon.
With the likes of Marcus Rashford, Anthony Elanga and Jadon Sancho at his disposal, Rangnick has the tools to launch dangerous counters while ensuring that his team remain compact and difficult to play through on the defensive side of the game.
His forwards are quick and vaguely comparable to the likes of Mohamed Salah and Sadio Mane, in terms of speed and directness, and United have picked up a number of positive results against Guardiola in the past, specifically under Ole Gunnar Solskjaer.
Ultimately, Liverpool's historic rivals could be set to support their quest for this season's Premier League title.
