Wellander, who "played an integral role in the Abba story," passed away, and the members of the band Abba posted a statement on their Instagram page expressing their sadness.
With songs like "Knowing Me Knowing You," "Slipping Through My Fingers," and "Eagle," the band's biggest hits in the 1970s and 1980s were played by lead guitarist Lasse Wellander.
Wellander, who was born in 1952 in the small Swedish village of Skrekarhyttan, picked up the guitar in 1963 after seeing the Beatles perform live on television.
Wellander previously played in the rock-blues group Nature, which toured with Ted Gärdestad, a Swedish singer-songwriter.
He first met the two male members of Abba—Björn Ulvaeus and Benny Andersson—during this period.
Wellander was a key member of the band throughout its live performances and contributed guitar to eight of their studio albums.
He played guitar on "Intermezzo No. 1" and "Crazy World" for the group's debut recordings together in 1974.
Wellander continued a solo career, producing and recording his own songs, when Abba disbanded in the early 1980s.
He did, however, continue to have close ties to Abba, contributing to the scores of the two Mamma Mia! film musicals and taking part in the band's 2021 comeback album, Voyage.
Wellander succumbed to cancer on Friday. He was in his seventys.