Mamma Mia – here we go again! The four members of Swedish pop group Abba have performed together on stage for the first time in more than three decades.

The unexpected performance at a private gala in Stockholm on Sunday celebrated the 50th anniversary of the day songwriting duo Bjorn Ulvaeus and Benny Anderson met for the first time, paving the way for Abba’s global success.

The Herald:

They were joined by former band mates Agnetha Faltskog and Anni-Frid Lyngstad for a surprise performance of 1980 hit Me and I.

It is the first time the group has performed publicly since their acrimonious split in 1982, and seems to be part of a softening of relations.

“It’s been a great night,” Benny reportedly told Sweden’s Expressen newspaper.

“It was absolutely amazing – a lot of emotions,” Anni-Frid agreed. “We’ve made this journey throughout our history. Benny and Bjorn in particular. It’s been very nostalgic.”

The performance comes after the four former members of Abba reunited for the first time in almost a decade back in January, joining forces for the opening of a Stockholm restaurant inspired by the Mamma Mia! musical.

Benny, Agnetha and Anni-Frid showed up for the opening night of Bjorn’s Greek taverna.

ABBAThe band on their way to a press conference in London on 1974 (PA)

But they turned down requests to sing and denied they could ever get back together, dashing fans’ hopes.

The foursome have always adamantly refused to reform, despite rumours they were offered $1 billion (£690 million) to do so after the sucess of the musical Mamma Mia! which was made into a movie starring Meryl Streep.

In 2014, Bjorn said: “We took a break in `82, and it was meant to be a break. It’s still a break and will remain so. You’ll never see us on stage again.”

Abba also will not reunite for the money, money, money.

He added: “We don’t need the money, for one thing. Usually the reason bands have reunions is that one of them is destitute and the others want to help. Fortunately that has not happened to us.”