The musician was joined by bandmate Benny Andersson to reflect on the Swedish group's lasting impact as their show ABBA Voyage marked two years in London.
Avatars of Ulvaeus, Andersson, Agnetha Faltskog and Anni-Frid Lyngstad perform all their biggest hits to full houses in a specially made arena in the Queen Elizabeth Olympic Park.
"It's very hard to understand. Maybe impossible," Bjorn Ulvaeus says of ABBA's lasting legacy. (AP PHOTO)
Ahead of the show on Monday night, the 756th since it launched, the duo answered questions from celebrity fans in the audience, including actors Dame Joanna Lumley, Matt Lucas and Rosamund Pike, as well as musicians Rick Astley and Sharleen Spiteri.
Reflecting on the band's impact, Ulvaeus said: "It's very very hard to grasp emotionally that we wrote these little songs and it gave rise to this and the millions of people we have touched.
"We know it's true but it's very hard to understand. Maybe impossible."
Andersson added: "I've seen the show so many times and I think we look good up there ... but I have no idea what it really is that makes people have it in them to want to listen to music that was done 50 years ago, 40 years ago, 30 years ago."
ABBA Voyage features 21 of the group's biggest hits, including Dancing Queen, Waterloo and Mamma Mia, and has already been seen by two million fans.
Ulvaeus said: "Back in '79, I don't think we ever thought about being listened to in 10 years' time.
"If you said something like this would happen in 50 years' time, it would be preposterous, it just doesn't happen."
Despite their prolific output, the duo have never collaborated with other artists but Andersson said he would not rule it out.
Asked if they would ever work with someone like Dua Lipa or Lana Del Rey, Andersson said: "I would say I will take a look. We have been asked but never done it."
Still looking great: ABBA arrive for the ABBA Voyage concert in London in 2022. (AP PHOTO)
Reflecting on their biggest successes over the course of their lives, Andersson mentioned being inducted into the Rock N Roll Hall of Fame in 2010.
He said: "There are a moments when you know you've written a good tune. It doesn't happen often."
Meanwhile, Ulvaeus highlighted ABBA's Eurovision victory 50 years ago with Waterloo.
He said: "It has to be said, the feeling when you realise the whole world knows about it and the possibilities and the potential."
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