ABBA with Ted Gärdestad.
Please read the link about Ted and his connection with the ABBA members. It's very sad, but he (and his brother) were very talented. Agnetha attended his funeral in 1997 in Sollentuna (where I grew up).
Björn and Benny produced a lot of his stuff and both Agnetha and Frida sang back up vocal on his recordings.
Search YouTube to see him perform.