"I thought, why not come and play for Magdalena?" Benny Andersson said from a piano set up at the Social Democrats' party headquarters, hours after polls opened.
The 79-year-old then launched into the melody of the famous song as supporters gathered in central Stockholm.
"Mag-da-le-na!" the crowd sang along, instead of "Mamma Mia", to the amusement of Andersson, leader of the opposition Social Democrats.
Swedes are voting in a tight race that will see either the left-wing opposition reclaim power or the far right enter government for the first time.
The songwriting genius said he normally avoided being used as kuttersmycke, literally a figurehead on a ship. "But this time I thought, if that’s what I am, then I may as well be it," he told TT.
"If I can contribute in any way to making it go well, I want to do it. I don’t think it will help much, but I’ll do it anyway."
Here's a video posted by former foreign minister Ann Linde:
https://t.co/tknqC2nGG2
— Ann Linde (@AnnLinde) September 13, 2026