LISTEN: Sia Shares Song She Wrote With Adele

Pop singers Sia and Adele are two songwriters of the highest caliber, so it's no surprise the two tunes they've penned together are pretty special -- even if they didn't make it onto Adele's upcoming 25 album.

The good news is Sia will include both songs, the previously shared "Alive" and, now, "Bird Set Free," on her next album, This Is Acting, a collection of songs she wrote with and for her peers.

Written by Sia, Adele, and Tobias Jesso Jr., "Bird Set Free" is a personal victory song, one that's not "going to care if I sing off-key."

And by all accounts, it was a blast to write. Adele said in her recent Rolling Stone interview that she and Sia had fun working together in the studio.

"I actually love the dynamic of us both being in there and just fucking being bossy. And it's all these male producers, and they're all fucking shitting themselves 'cause we're in there," Adele said.

Listen to Sia singing "Bird Set Free" below.