Even though Taylor Swift plans her surprise guests months before they take the stage with her, the A-list celebs are always a treat for the unsuspecting fans. At last night's Speak Now show in Taylor's hometown of Nashville, Tenn., Paramore songstress and fellow Nashvillian Hayley Williams took the stage to perform 'That's What You Get' for a sold out crowd.

Before Hayley made her official appearance, the 'Mean' singer teased and taunted her fans, suggesting that some of her famous friends might be hiding backstage. Not knowing what to expect, the Swifties screamed and cheered, anxious to see who would come out. "My friend Hayley has this band called Paramore..." Swift said slyly, trailing off as the song started and the red-headed rocker walked onto the platform.

The pair launched into the 2008 Paramore chart-topper, though Taylor stayed back a little to let her friend steal the show. Hayley bounced across the stage and pumped up the Bridgestone Arena crowd -- though it seemed as if the whole city was there to sing along.

Following the concert and a full night's rest, Hayley tweeted, "Got to sing "That's What You Get" with my friend @taylorswift13 & her amazing band last night! Thx to everyone who sang along :) #nashville"

But Taylor didn't let the curtain close without offering the country fans in the house a nice gift. Brooks and Dunn legend Ronnie Dunn took the stage with the 21-year-old pop-country phenomenon to perform his hit solo single, 'Bleed Red.' Check out that all-star performance here.

Watch Taylor Swift and Hayley Williams Perform 'That's What You Get'