Early in 2014, Miley Cyrus tweeted a birthday shout-out to Flaming Lips ­frontman Wayne Coyne, a favorite of hers since the Hannah Montana days. He sent her his number in response, kicking off one of the most surprising musical friendships in recent history. Since then, Cyrus, 22, has had The Lips join her onstage on her Bangerz Tour, appeared on two Beatles covers by the band and even got matching tattoos with Coyne and his girlfriend. "We've just been getting in each other's worlds," Coyne, 54, tells Billboard. "We text every day -- sometimes three times, sometimes a thousand."

The Flaming Lips' Wayne Coyne Talks Collaborating With Miley Cyrus: 'We're Either Ruining Each Other or Helping Each Other'

Now, Coyne reveals, Cyrus and The Lips are prepping a disc of seven songs that they wrote and recorded together during the last year. No release date has been set, but the tracks are nearly done; Coyne and Lips guitarist Steven Drozd are mixing them in their Oklahoma City studio. "She does the pop thing so great, so it still feels pop, but a slightly wiser, sadder, more true version," Coyne says of the project. "Some of it reminds me of Pink Floyd and Portishead." (Cyrus wasn't available for comment.)

Despite their backgrounds, Coyne says he and Cyrus are more similar than one would think. They share a candy-colored, ­psychedelic aesthetic and a deep love of rock and pop history, and they both have a ­forthright, authentic vibe, one of the things that most attracted him to her. "I saw her a couple times where she was overcome with emotion, like when her dog died," he says. "That really pierced me. She realizes she's Miley Cyrus, but she doesn't act like she's all powerful." Plus, he adds, "she can f---ing sing. She can do 100 takes, and they'll all be different and good."

Watch Miley Cyrus in the Studio with Wayne Coyne

The tracks were written and recorded at The Lips' studio and Cyrus' Los Angeles home in stripped-down, DIY fashion. "Her studio is just a little room with a desk," says Coyne, "and Miley was sitting there mixing. I was like, 'I can't picture Beyoncé? doing this!' It's not a ­putdown of Beyoncé. I just don't see her recording her own vocals and then EQ'ing it. It's so punk rock!"

This story originally appeared in the May 9 issue of Billboard.