The 24-year-old rapper and 33-year-old singer shared the single after it leaked online Saturday. Azalea had teased the collaboration in March, telling MTV News the track is a true, "powerhouse" duet.
"I'm really really happy to see so many people loving it but i also just want to clarify its not an 'early' release," the rapper tweeted following the leak. "Also for the record brit and i are both singing the chorus's together... i guess you guys aren't used to hearing my singing voice."
"Pretty Girls" will appear on Spears' upcoming ninth studio album, and she and Azalea will perform the song at the 2015 Billboard Music Awards on May 17. Spears last released Britney Jean in November 2013, while Azalea debuted The New Classic in April 2014.