SINGAPORE - American singer Taylor Swift has confirmed in her Disney+ concert film that her boyfriend, English actor Joe Alwyn, contributed to her songs on Folklore under the pseudonym William Bowery.

"William Bowery is Joe," said the singer in Folklore: The Long Pond Studio Sessions, confirming months of fan speculation that it was the 29-year-old actor who has been with Swift, 30, for three years.

"Bowery" was credited under two tracks on her surprise July album.

Swift said Alwyn wrote the first verse and entire piano part on Exile, and originally sung the part of the duet that was eventually recorded by Bon Iver's Justin Vernon.

He also co-wrote the song Betty after she heard him singing "the entire fully formed chorus from another room".

In the film, she performs songs from the album and discusses its creation under lockdown.

She recalls that Betty was the first time she brought up the idea of the two making a song together.

"I was like, 'Hey, this could be really weird and we could hate this because we're in quarantine and there's nothing else going on, could we just try to write this song together?'" she says of her conversation with Alwyn.

Folklore has been nominated for six Grammy Awards including Album of the Year, while the song Cardigan is up for Best Pop Solo Performance and Song of the Year.

Last month, Billboard reported that Folklore became the first album to sell a million copies this year.