"Never Again" was written by Swedish singer and songwriter Tomas Ledin. He had already worked with ABBA, he recorded for the same label and he Tomas toured with them as a backing-singer in 1979 and 1980.

In Sweden, he was very successful but he had not had success in the rest of Europe. Stig Anderson the owner of Polar Music believed in his singing abilities and wanted to promote him across the continent. When he first heard "Never Again" Stig thought this song would make a good duet. He also knew who should become Tomas' singing partner. ABBA were in their summer holidays and member Frida had just recorded an album on her own so Stig thought that Agnetha Fältskog who wasn't involved in any ABBA projects at the moment had the right voice for the song.

Agnetha and Tomas recorded this song together, although they were not together in the studio when they laid down their vocal tracks. The single was quite successful in European countries like West Germany, mostly due to Agnetha's appearance. This song is Tomas Ledin's only successful single outside Sweden.

The two also did a Spanish recording entitled "Ya Nunca Más" which was a big hit in Chile and other South American countries.

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Wikipedia