Robert Lewandowski is now unquestionably the world's best striker.

The Polish striker was utterly ridiculous in the 2019/20 season.

In that campaign, Lewandowski scored 55 goals in 47 games as his goals helped Bayern Munich dominate in Germany and in Europe.

His form hasn't dropped off this season, either, with the 32-year-old netting 23 goals in 20 games so far this season for Bayern.

It wasn't at Bayern that Lewandowski emerged as one of the world's best strikers, though.

Jurgen Klopp and Robert Lewandowski

It was under Jurgen Klopp at Dortmund where Lewandowski made a name for himself.

Klopp signed the little-known Polish striker in 2010, with Der BVB paying €4.5 million for his services.

The two would go on to form quite the partnership at Dortmund.

Lewandowski has now opened up on his relationship with Klopp in an interview with The Players' Tribune.

He recalled a brilliant bet that Klopp made with him soon after he joined the club.

Robert Lewandowski

"I once made a bet with Jürgen Klopp," he started.

"It was 2010, and I had been a few months at Borussia Dortmund. Honestly, it was so tough. When I arrived I could barely speak a word of German. I knew danke. Thank you. I knew scheisse. The weather was rainy and grey. And with Klopp, the intensity in training was very, very high.

"I was desperate to make my mark, and Jürgen wanted to challenge me.

"So in the first few months we made a little bet.

"If I scored 10 goals in a training session, he’d give me 50 euros.

"If I didn’t, I’d give him 50 euros.

Jurgen Klopp

"The first few weeks, I had to pay up almost every time. He was laughing. But after a few months, the tables turned. I was the one raking in the cash.

"So one day he said, “Stop! O.K.! That’s enough. You’re ready now.”

And ready he was. Lewandowski went on to score 103 goals in 187 games across four season for Dortmund.

Lewandowski went on to explain his relationship with Klopp, who he described as a 'father figure' as well as a 'bad teacher'.

"Jürgen was not only a father figure to me. As a coach, he was like the “bad” teacher. And I mean that in the best sense of the word.

Jurgen Klopp in action for Dortmund

"Let me explain. Think back to you when you were in school. Which teacher do you remember the most? Not the one who made life easy for you and never expected anything from you. No, no, no. You remember the bad teacher, the one who was strict with you. The one who put pressure on you and did everything to get the best out of you. That’s the teacher who made you better, right? And Jürgen was like that.

"He was not content to let you be a B student, you know? Jürgen wanted A+ students. He didn’t want it for him. He wanted it for you.

"He taught me so much. When I arrived at Dortmund, I wanted to do everything quickly: strong pass, one touch only. Jürgen showed me to calm down — to take two touches if necessary.

"It was totally against my nature, but soon I was scoring more goals.

"When I had that down, he challenged me to speed it up again. One touch. BANG. Goal. He slowed me down to speed me up. It sounds simple, but it was genius, really."

Maybe the two will link up at a club once again before they both retire.