Fans piled online to celebrate the long-awaited news of the reunion of one of the world's most successful bands. "2021 has been saved by new ABBA music," @elliemiles23 said in one widely shared Twitter post.
The album "Voyage" would come out on 5 November, the band said during the livestreamed launch. They released two of its 10 songs - "I Still Have Faith In You" and "Don't Shut Me Down" - on Thursday.
"First it was just two songs," songwriter Benny Andersson said. "Then we said 'maybe we should do, I don't know, a few others. What do you say girls?' And they said 'yeah' and then I asked 'why don't we do a full album?'"
"I knew when Benny played the melody it just had to be about us," co-songwriter Bjorn Ulvaeus said about "I Still Have Faith In You".
"No imagination could dream up that, to release a new album after 40 years and still be the best of friends and enjoy each other's company, and have total loyalty."
The concerts will be held at a purpose-built ABBA Arena in London's Queen Elizabeth Olympic Park in May next year, and feature digital versions of its four stars, Agnetha Faltskog, Bjorn Ulvaeus, Benny Andersson and Anni-Frid Lyngstad.
The "abbatars" were created using motion capture technology - similar to that used to create Gollum in the movie series "Lord of the Rings" - and will show members of the band as they looked in 1979. They will not be holograms, the band said.
"The only big problem was that we had to shave our beards," Benny Andersson said on the livestreamed broadcast.
Rumours swirled for years that the group would get back together, but the members turned down a string of offers, including one reported $1 billion package to tour again.
ABBA was founded in the early 70s by then couples Agnetha and Bjorn and Benny and Anni-Frid. Their initials gave the band its name.
They sold more than 385 million albums and topped charts from Australia to America with a string of hits including "Waterloo", "Dancing Queen" and "Take A Chance On Me".
The concert concept was created by the band and Industrial Light and Magic, the special effects company founded by George Lucas to make the original Star Wars-movies, the band said.