It was ladies' night on Friday, as an all-female lineup kicked off the first evening of the 4th ACM Party for a Cause at the Las Vegas Festival Grounds. The group, which included Cam , Martina McBride , Maddie & Tae , Brandy Clark and more, had a few surprises up their sleeves.

Carrie Underwood and an all-female cast kicked off the Academy of Country Music’s fourth annual ACM Party for a Cause festival Friday (April 1) in Las Vegas. Miranda Lambert pops in as a surprise guest during Carrie Underwood's performance.

The two performed Lambert's hit, "Something Bad," together, and judging by the posts the country stars' friends and fans later shared on social media, it was quite the memorable collaboration.

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Carrie Underwood, Miranda Lambert