The story begins back in 2003.
It had been a disappointing first half of the season, so 89 Unioners jumped the fences of the Stadion An der Alten Försterei on the day before German Christmas, with flasks of steaming mulled wine and biscuits, to sing some Christmas carols.
It was to remind themselves of why they always came back to Union. That sense of community.
And the number of attendees has grown from year to year - more than 10,000 attended the Weihnachtssingen in 2010. More than 30,000 came in 2022. Union's famous Christmas tradition has become something which unites people of different generations, and even of different football clubs.
Father Müller recites the Christmas story. The choir of the Emmy-Noether-Gymnasium set the tone and the tune. A small brass band accompany them, and everyone else just sings along, as loud or as quietly as they like. The songbook and candle are free of charge of course, though a small donation for the club's youth work is obviously greatly appreciated.