What started as a seemingly far-fetched transfer rumor has now become reality and, for Mats Hummels and Borussia Dortmund, it's all come full circle.

Following three trophy-laden seasons in Munich, the 30-year-old is set — pending a medical — to rejoin BVB, the club that first gave him a platform to carve out his spot among the best in the world.

With his stock in Bavaria falling and Dortmund desperate to topple the record titleholders, Hummels' return comes in strikingly similar circumstances to those of when he first swapped Bayern for Borussia in 2008.

Once again there are risks involved. Once again though, Dortmund boast the bigger potential upside in the deal.

Dortmund's daring summer

Fresh from missing out on a sixth Bundesliga title despite racking up their third-best points tally in Bundesliga history, BVB have wasted little time in setting themselves up for another title tilt in the 2019/20 campaign.

"We weren't missing much in the end, but 'much' is more important than we think," admitted head coach Lucien Favre, who signed a one-year contract extension just a day before news of Hummels' deal broke.

"The work we're doing is important. We've got to keep working hard and cleverly — with all of our players. No one knows what will happen in the summer break."

Fast forward a month and the image of Dortmund's 2019-20 challengers is already coming into focus. Nico Schulz, Julian Brandt and Thorgan Hazard have all been drafted in to add yet more pedigree.

Meanwhile, the capture of Hummels is the latest major move by a side intent on going a step further after finishing just two points behind Bayern Munich at the close of play last season.

Read more:  Thorgan Hazard, Julian Brandt, Nico Schulz: Borussia Dortmund buy big and early

Missing puzzle piece?

Going forward, BVB almost always had the individual ability to carve out and convert chances, which saw them end the campaign as the league's second highest-scoring side behind the title winners. It was at the back where they suffered most.

A spate of injuries that seemed never-ending — during the second half of the season especially — led to Favre using 16 different variations of a back-four over the course of 34 Bundesliga games.

As a result, consistency was hard come by for a backline that regularly had an average age of 23 years or younger. And that's where Hummels comes in.

Not prone to extended spells on the sidelines in recent years, the 70-time German international brings with him a wealth big-game nous as well as playmaking ability and composure on the ball, all qualities that Dortmund's defense lacked.

BVB have a trio of talented young center backs on their books in Manuel Akanji, Abdou Diallo and Dan-Axel Zagadou. All three have room to grow from the good and the bad of a roller-coaster campaign, but Hummels has the potential to be an influential learning aide; he could accelerate their development.

The Bayern academy graduate's quality was called into question by both club and country last season. Now he has a chance to prove that reports of his decline were greatly exaggerated as he looks to shape the future of the Black and Yellows.

Read more: DW's summer transfer window roundup

Risk versus reward

When Hummels moved to Dortmund for the first time in 2008 (joining on a permanent basis in 2009), he arrived as an unproven youngster, who hadn't made a breakthrough in Bavaria.

Now the 30-year-old returns as a center back entering the tail end of his career with his pace waning. But his first challenge will be to build bridges with a fan base whose hearts he broke back in 2016 when he followed Mario Götze and Robert Lewandowski to Munich.

Leaving as the active captain wasn't the most amicable of departures and Hummels will have to overcome any early resistance if he wants to win back the BVB faithful. Just like out on the pitch though, he is rarely one to shy away from a challenge.   

"He's really wants this, otherwise he wouldn't have done something like this," said sporting director Michael Zorc to Funke Sport. "It's not an easy step to take. It's another revamp for him. I like it."

Success will ultimately be the best tonic to heal any lingering heartbreak following Dortmund's most significant summer signing. BVB have accepted the risk in the hopes of reaping rewards and, in Hummels, have made a prudent bet on a player that fits their current mold: dynamic, bold and with a point to prove.