LONDON — Abba's Bjorn Ulvaeus reflected on the Swedish pop group's reach and longevity as he joined Mamma Mia! cast and creators for the musical's 25th anniversary celebrations in London on Saturday (April 6).

Saturday also marked 50 years since Abba won the Eurovision Song Contest final in Brighton, United Kingdom, in 1974 with the song Waterloo, bringing them to global attention.