Nearly four decades after disbanding and vowing never to get back together, Swedish superstars ABBA were expected to announce a comeback on Thursday with new songs and performances by holograms called “Abbatars”.

Almost as famous for their over-the-top outfits as their music, the group have notched up over 400 million album sales over 50 years.

They had a string of hits in the 1970s and early 1980s after winning Eurovision in 1974 with “Waterloo”.

Since parting ways in 1982 they have resisted all offers to work together as a foursome.

But later on Thursday, they are expected to delight fans with news on a fresh collaboration.

The now septuagenarian stars of pop classics such as “Dancing Queen”, “The Winner Takes It All” and “Take a Chance on Me”, said they would make a “historic” announcement at 16:45 GMT.

Details are still under wraps but the group is expected to announce their first new songs since the 1980s, as well as the launch of a new theatrical show in which they will perform as digital avatars — or Abbatars.

Last week, the group — Anni-Frid Lyngstad, 75, Agnetha Faltskog, 71, Bjorn Ulvaeus, 76, and Benny Andersson, 74 — announced on Twitter: “Thank you for waiting, the journey is about to begin.”

A website called AbbaVoyage.com promises a “historic livestream” and Universal Music Group, which owns the band’s back catalogue, was set to hold an event at an east London observation tower.