Here’s an interesting grouping that you probably never expected to see: Sean Lennon (son of John Lennon and Yoko Ono) has released a song with Willow Smith that was cowritten with the late Carrie Fisher.

Lennon revealed on SoundCloud that he and longtime friend Fisher wrote a twinkling tune called “Bird Song” years ago, and that after the actress’s death in December, he felt he “had” to record and release it. “Carrie and I used to stay up til dawn chatting and pontificating about life. They were my best moments,” he wrote.

He recruited Smith — whom he calls “a prodigal angel” with a “golden voice” — to add her vocals to it, and the result is a serene piano ballad about “staying up too late and hearing the birds sing.” The unmixed demo was recorded in only a few hours, Lennon wrote, but it’s dreamy, affecting stuff nonetheless.

Lennon and Smith’s unexpected collaboration comes just a few weeks after he shared photos of them in a recording studio. Looks like we finally know what magic they were cooking up together.