On 12 May 2012, Jurgen Klopp's Bundesliga champions Borussia Dortmund beat Bayern Munich 5-2 in the German Cup final to complete a domestic Double.

At the western end of Olympiastadion in Berlin, tens of thousands of Dortmund supporters had recreated the Yellow Wall beneath a huge banner featuring the final line from a popular terrace chant: "Werdet uns're Helden!" – become our heroes!

Stood beneath the banner, yellow and black scarf tied around his neck, was the 29-year-old assistant coach of Dortmund's Under-17s, a semi-pro striker by the name of Edin Terzic.

Nine years later, at the end of the pandemic-afflicted 2020-21 season, Terzic would lift the German Cup himself as Borussia Dortmund's interim coach.

And on Saturday, he will lead his boyhood club out at Wembley in the Champions League final against Real Madrid, hoping to do what it said on that banner in Berlin and become a bona fide Dortmund hero by lifting the ultimate prize.

They were last here in the 2013 showpiece when Klopp's Dortmund were beaten 2-1 by Bayern Munich through an 89th-minute Arjen Robben strike.

"Last time, I travelled to London the day before to try and soak up the atmosphere before supporting the team from the stands," Terzic told BBC Sport on the final day of the Bundesliga season. "But those days are over."

Now 41, Terzic's journey from season-ticket holder to head coach is as romantic as they come – but it's also been an emotional one with triumphs outweighed by setbacks.

Not least on the final day of last season when, needing only to beat mid-table Mainz at home to seal a first Bundesliga title since 2012, Dortmund spectacularly choked.

After drawing 2-2 to hand Bayern Munich an 11th consecutive title, Terzic stood in tears as the massed ranks on the Südtribüne – the Westfalenstadion's famous south stand – sang in appreciation of one of their own: "Wir sind alle Dortmunder Jungs!" – we are all Dortmund lads!

Terzic's commitment to his club has never been in doubt – but his suitability for the job has on several occasions, including twice in the last six months.

After Dortmund ended 2023 with a series of six games without a win, culminating in an insipid 1-1 draw at home to Mainz [again] which left Die Schwarzgelben six points off the top four, chief executive Hans-Joachim Watzke and sporting director Sebastian Kehl convened crisis talks – and decided Terzic would remain in charge.

But they also recruited former players – and 2013 Champions League finalists – Sven Bender and Nuri Sahin as assistant coaches, a move which raised eyebrows as to Terzic's authority, especially given Sahin's public ambitions to be a head coach himself.

Still, with Sahin immediately taking over attacking drills at a winter training camp in Marbella and Bender responsible for the defence, Dortmund's form picked up – at least until March when defeat at home to Hoffenheim again put Terzic under pressure before a 2-0 win at Union Berlin again saved his job.

While Dortmund's Bundesliga form has remained patchy, ultimately finishing a disappointing fifth, 27 points behind champions Bayer Leverkusen, Terzic has excelled in the Champions League.

"Unfortunately, the history of Borussia Dortmund shows us that we need to over-perform in one competition to win titles and this usually means that another competition suffers," he explained, revealing the sort of historical knowledge that only a fan can produce off the cuff.

He's right. When Dortmund won the Champions League in 1997, they finished third in the Bundesliga – eight points behind Bayern. In 2013, the gap was 25 points. Conversely, when Klopp won back-to-back titles in 2011 and 2012, they were knocked out of Europe in the group stage.

This season, Terzic led Dortmund successfully through a daunting group, including home and away wins over Newcastle United, victory over AC Milan in the San Siro and a draw with Paris St-Germain.

Their European excellence continued into the knockout stages, now boosted by two Premier League loanees - Chelsea's Ian Maatsen and, of course, Manchester United winger Jadon Sancho, back at the club where he'd made his breakthrough.

Sancho's final game for Dortmund before joining United had been that 2021 German Cup final under Terzic, whose undisputed man-management qualities are again benefitting the Londoner after a difficult time in Manchester.

"Jadon and I both know that he's not yet at his maximum level," said Terzic in April. "But we knew that and took it into account when we brought him back here. We see how hard he's working and we're sure he'll hit top form again soon."

Which is exactly what Sancho did, producing a man-of-the-match display in the Champions League semi-final first leg against PSG and setting Dortmund on course for the final.

At full-time after the second leg in Paris, Terzic disappeared into the jubilant mob of Dortmund fans at the front of the away end. Those same fans who had picked him up on the final day of last season against Mainz.

"This is why we do it," he said afterwards. "We'd hoped for such scenes last season. Unfortunately, it didn't go as planned but our fans were there for us. Today, we could give them a little bit back."

Terzic and Dortmund remain a mystery. "Who can work out Jeckyll and Hyde Dortmund?" asked tabloid BILD, stating: "Terzic is unsackable now."

And for local broadcaster WDR, Dortmund's progression to the final is already "the triumph of a beleaguered coach".

And what about the fans? Sitting on the train to Dortmund's last game of the season, one BVB supporter admitted he "would have sacked him at Christmas, but how can you criticise a coach who's taken us to the Champions League final?"

The mixed feelings were replicated around the beer stands under the Südtribüne. "He's brilliant, he's one of us," added another. "But as a coach…?"

Terzic was a fan at the Olympiastadion in 2012. He was a fan at Wembley in 2013. As he said, however, "those days are over."

Now, he wants to be seen as Terzic, the Borussia Dortmund head coach.

"Is there anyone who works in football who wasn't once a fan?" he asked, rhetorically.

"Whether journalist, steward or press officer, we all fell in love with football as fans and we all had a team which we loved and supported. My path as a fan led to me becoming head coach of Borussia Dortmund. I'm very happy about that. And very proud."

And whatever happens at Wembley, he's sure to remain what the banner at the Olympiastadion called for - a Dortmund hero.