In our latest feature retelling a story from each of our successful European campaigns ahead of the return of Champions League football this month, we detail a familiar face we encountered during the greatest triumph of them all, and contemplate how things might have turned out very differently...

‘I keep thinking about that missed chance because had I scored it could have been completely different for us. Unfortunately it did not go in and nothing can change that.’

Chelsea's run to glory in the Champions League in 2011/12 contained no shortage of ‘what if?’ moments, but perhaps the first was in the 57th minute of our opening game in the competition that year.

What if Michael Ballack, of Bayer Leverkusen, had scored when put clean through at Stamford Bridge, his former home? What if the German visitors had gone 1-0 up, rather than see Petr Cech perform heroics to keep out an old team-mate?

Earlier in the evening, before kick-off, Chelsea supporters gave Ballack a wonderful reception, and Chelsea Chairman Bruce Buck handed over a commemorative plate to mark four years of dedicated service.

On the hour, shortly after his missed chance, Ballack was subbed off. Barely 30 seconds later David Luiz fired us in front, and the Blues eventually ran out 2-0 winners against a side playing their first Champions League game in six years.

The teams reconvened in Leverkusen a couple of months later, Chelsea two points clear of their German opposition. Didier Drogba put us ahead early in the second half, before Cech and Ballack – both wearing protective masks – went face to face twice in a minute.

‘I was a little unlucky, Petr made two great saves,’ said Ballack after our legendary goalkeeper first tipped an overhead kick to safety, then bravely blocked a point-blank strike.

This time the missed opportunities didn’t prove costly for Leverkusen, as they fought back to win 2-1. It left them in pole position to qualify in first place from Group E.

On the occasion of his 100th European game, Ballack diplomatically expressed an unusual feeling in conquering a former team, before wishing Chelsea luck in qualifying for the knockout stages.

To do so we had to beat Valencia at the Bridge, and a brace from Didier Drogba set us on the way to a comfortable 3-0 victory that made sure of our place in the last 16.

In the group’s other game that night, another sliding doors moment played out.

What if Leverkusen had won against Genk, rather than unexpectedly drawing and handing us top spot?

Watch the story of our Champions League triumph in 2012 in the Fifth Stand app! Head to the Watch section and scroll down to Champions League Years, which tells the story of each our campaigns in Europe's elite competition...