Thirty-seven-year-old goalkeeper Weidenfeller called time on his career at the end of the 2017/18 campaign after making 349 Bundesliga appearances for the club across a 16-year span, seven of which intersected with Klopp's tenure at BVB between 2008 and 2015.
Together, they won two Bundesliga titles, the DFB Cup and reached the final of the UEFA Champions League in 2013, and will now be reunited at the Signal Iduna Park one last time.
📣 A GRANDIOS ÜBERRASCHUNG! 📣— Borussia Dortmund (@BVB) 27 July 2018
Schaut mal, wer sich für Roman Weidenfellers Abschiedsspiel am 7. September angekündigt hat! 😍
Wer von Euch ist noch dabei? 🎫 Tickets: https://t.co/KI3notXGJg pic.twitter.com/RUUwfHbzLW
In a not-so-carefully scripted video taken pitch side ahead of Dortmund's 3-1 victory over Liverpool in the ICC in Charlotte, North Carolina last week and posted on Dortmund's official Twitter account, Klopp is seen approaching Weidenfeller, saying wistfully: "I'd love to play again."
The former BVB No1 replies: "I've got a great idea. Why don't you come along to my farewell match on 7 September?"
Klopp beams as he replies: "Anyone who wants to see Klopp and Weidenfeller in action together will have to get a move on because we're not the youngest anymore. It's going to be a 'grandios' testimonial."
Watch: Klopp - Made in the Bundesliga
Indeed, that is the overall slogan of the match, a tongue-in-cheek nod to one of Weidenfeller's most memorable moments at Dortmund.
After winning the 2011 Bundesliga title, Weidenfeller gave a post-match interview to a visiting broadcaster at the Signal Iduna Park: "I think we have a grandiose saison gespielt [we've had a great season]," he said, mixing up German and English to much hilarity. So much hilarity, in fact, that to honour his career, Dortmund fans have produced t-shirts reading, "You have 16 grandiose saisons gespielt [you had 16 great seasons]." Klopp called it a comment that would "go down in history".
Weidenfeller is only eighth Dortmund player in history to be granted a testimonial, which will be played during the first international break of the 2018/19 season. In addition to Klopp, other confirmed participants are Michael Ballack, Torsten Frings, Marcio Amoroso, Ewerthon, Dede, Sebastian Kehl, the Bender twins Sven and Lars and Kevin Großkreuz.