Taylor Swift has joked she is now officially "the fourth Haim sister", after collaborating with the band on a remix of their track, Gasoline.
"Cancel the DNA test," wrote the singer online. "I'm the 4th Haim sister and this song is the only proof I need".
The song appears on the new expanded version of the Los Angeles band's album, Women In Music Pt. III.
The Grammy-nominated siblings said it was their famous friend's favourite on the original 2020 record.
They noted how the new version had allowed them to "reimagine" the track.
The mood board for the gasoline remix is just this one photo pic.twitter.com/G4ziCaPond— Taylor Swift (@taylorswift13) February 19, 2021
"Since we released wimpiii in June, Taylor had always told us that Gasoline was her favourite," they posted on Instagram, around Friday's release.
"So when we were thinking about ways to reimagine some of the tracks from the record, we immediately thought of her.
"She brought such amazing ideas and new imagery to the song and truly gave it a new life."
Este, Danielle and Alana Haim then thanked the star - who recently re-versioned some of her own songs, as part of an attempt to regain control of her music - for lending her "incredible voice and spirit to a track".
Fans have been sharing the new rendition of the slow-grooving, brooding and lust-filled number widely since it dropped overnight.
"Taylor Alison Swift, you singing 'you needed ass' has just revived me since my death by Love Story experience," posted one fan, referring to the suggestive lyrics.
Another noted the current trend for fuel/car-driven metaphors in modern pop.
Taylor Swift have her Getaway car. Olivia Rodrigo got her Drivers Licence, and HAIM have their Gasoline — They are all ready to GO! pic.twitter.com/1dDvh750vI— cassiopeia 💛💛 (@snake_stones) February 19, 2021
A third fan was so obsessed with the musical hook-up that she started seeing visions of the four US musicians in her food.
taylor swift singing on gasoline remix with haim pic.twitter.com/hZFNsM4Fiu— tiler (taylor’s version) 🤍💫 (@weranwithwolves) February 18, 2021
Haim, who teased the collab earlier in the week, previously featured on Swift's track No Body, No Crime, from her own 2020 album, Evermore. Now she has returned the favour.
And while it's all friendly at the moment, the artists will actually be rivals at next month's Grammy Awards, with Women in Music Pt. III and Swift's Folklore both up for the album of the year prize: a true test of their newfound official sisterhood.
Who else has Swift collaborated with?
It would almost be quicker to say which stars Swift hasn't collaborated with...
She first duetted with another of her close songwriting buddies, Ed Sheeran, on the song Everything Has Changed, for her 2012 album Red.
The rather lovely folk-pop ballad found the pair singing about wanting to get to know a lover better.
Its loveliness was matched only by the video of two young lookalikes hanging out together.
Swift and Sheeran would come together again years later on End Game, from her 2017 record, Reputation. This time around though, Sheeran flexed his rapping muscles while on an epic international bender with his talented pal, and US rapper/singer Future.
Another British singer, Zayn, of One Direction fame, joined her on the 2016 track, I Don't Wanna Live Forever.
This one was made for the erotic romantic drama film Fifty Shades Darker, and found the singers indulging in a battle of the falsettos.
Prior to that, Swift got to work with one of her all-time musical heroes, Imogen Heap, on Clean.
The innovative UK singer-songwriter provided backing vocals and also co-wrote/produced the closing track on Swift's 2014 album, 1989.
It remains one of her most experimental and electronic offerings to date.
And finally, while we could go on, Compton rapper Kendrick Lamar appeared most memorably on the same album, helping Swift to best convey the Bad Blood she had with another unnamed singer.
We can't say for sure who this one is about (although we could probably guess, right Swifties?) but it's clearly not about Haim. They've got good blood.
The rather explosive visuals won the Grammy award for best music video.