Billie Eilish Explains New Mullet Haircut, Says It Won't Stay for Long

Billie Eilish has a perfectly good explanation for why she's rocking what appears to be the Joe Dirt look ... and an even better one for why it'll only be temporary. Sorry, mullet fans.

We got the goth pop singer Tuesday at LAX, where we asked her about the new haircut she debuted the day before at the LACMA Art + Film Gala in L.A. ... which turned out to be all the rage among her fans and fashion experts alike. Hey, folks love them some '80s nostalgia.

Welllll, unfortunately for all those people who were loving it ... Billie here has an update they might not be so happy to hear. It was a fluke to begin with, and it ain't stayin'.

BE gives up the backstory on how the mullet even came to be, and it sounds like a salon appointment gone majorly wrong. And yes, as soon as she can grow some of her follicles back to original length ... Billie says America's favorite trashiest 'do will be no more.