Britney Spears & Iggy Azalea Perform 'Pretty Girls' at the 2015 Billboard Music Awards: Watch

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Britney Spears performs at the 2015 Billboard Music Awards on May 17, 2015 in Las Vegas, Nevada.

Britney Spears and Iggy Azalea's "Pretty Girls" collabo already gave us one of the summer's best music videos. And on Sunday night in Las Vegas, they delivered one of the most memorable performances at the 2015 Billboard Music Awards. 

2015 Billboard Music Awards

After beaming down onto the stage Star Trek-style, Brit & Iggy were joined by a crew of dancers dressed up as silvery space aliens and neon-toned '80s b-boy dancers. 

Britney's dancing was seriously on-point, and Azalea's sass was turned up to 11. As it should be. Watch a clip of it below.

Billboard Music Awards 2015