The 79-year-old Swedish singer, who has been married twice before, met Sas in Nuremberg, Germany in 2021 in connection with the release of Abba's last album Voyage.
A post to his Instagram page said: "Today on the 21st of September 2024, Bjorn Ulvaeus married Christina Sas from Herning, Denmark.
Bjorn Ulvaeus was married to bandmate Agnetha Faltskog, and Benny Andersson to Anni-Frid Lyngstad. (AP PHOTO)
"They met in Nurnberg in 2021 in connection with the release of Abba's last album Voyage and started dating in the spring of 2022.
"The wedding took place in Copenhagen in the presence of close friends and family.
"Sandi Toksvig, Anne Linnet and Kaya Bruel generously performed and made the evening extra special."
Ulvaeus posted a number of photos from the day, one of which showed QI host Toksvig dressed in red robes standing next to Ulvaeus, who donned a suit, and his wife Sas, who wore a muted green wrap dress.
This Morning's Gyles Brandreth said in a post to Instagram that he had "loved meeting ABBA's Bjorn Ulvaeus" and Sas for his Rosebud podcast.
He also claimed Toksvig had officiated the ceremony.
Ulvaeus is known for being one quarter of Swedish pop group Abba, who this year celebrated 50 years since their winning performance at the Eurovision Song Contest with their song Waterloo.
The group was comprised of two couples - Ulvaeus and Agnetha Faltskog, and Benny Andersson and Anni-Frid Lyngstad.
Faltskog and Ulvaeus, who married in 1971, divorced in 1980, while Andersson and Lyngstad divorced in 1981 - a year before the band split.
The quartet did not reform to perform at Eurovision 2024 despite the event being held in Sweden after Loreen won the competition in 2023 with her hit single Tattoo.
Ulvaeus was also previously married to Lena Kallersjo.
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