The Bundesliga giants were in the market for a new coach after seeing Peter Bosz and Peter Stoger fail to convince in the 2017-18 campaign.
Watzke decided to reach out to Klopp despite being fully aware that he was tied to a long-term contract at Anfield.
The approach came as something of a surprise to a man who had previously enjoyed seven memorable years with Dortmund – a spell which included two title triumphs.
In a new biography about Watzke called ‘Real Love: A life with BVB’, Klopp says of a call he took in May 2018: “At some point my phone rang while I was on the plane and Aki was on it: 'Jurgen, you have to come back'. I laughed, I thought he was kidding.
“'Are you stupid, have you been drinking? How do you get that idea, I have a few more years in Liverpool'.
“I do not know how serious he was at that moment, but I realised that he wanted me to be more willing to respond.”
Watzke admits that he always expected Klopp to knock back his advances, with a coach who would go on to claim Champions League glory with Liverpool in 2018-19 tied to a deal with the Reds through to 2022.
“I knew that Jurgen would say no and that he would fulfil his contract in Liverpool,” Watzke said.
“But if you want to go in a new direction, and we had to hit a new path at BVB at that point, then I had to at least ask Jurgen if it was a possibility.
“I did not expect it at all, but I would never have forgiven myself had I not at least asked him at that moment.”
While Klopp politely declined at that point in time, no door has been closed to Dortmund.
There is still plenty for the 52-year-old to achieve in England, as he sets his sights on a Premier League crown, but he has hinted at walking away when his current deal comes to a close.
If his services were then required by Dortmund at some stage, an emotional return to Signal Iduna Park could be made.
“As a rescuer at a time of need, if the club really needs my help, why should I not do it?” Klopp said.
“It's very nice that I even have the opportunity. But I do not think it's very likely to happen.”