Taylor Swift & Shirtless Jason Derulo Duet on 'Want to Want Me': Watch

Paul Morigi/LP5/Getty Images for TAS
Taylor Swift and Jason Derulo perform onstage during The 1989 World Tour Live at Nationals Park on July 14, 2015 in Washington, DC. 

Taylor Swift continued to show off her A-list pals at the 1989 tour stop in Washington, D.C. last night (July 14) -- this time, though, there was a little added sex appeal.

Watch Taylor Swift and Nick Jonas Sing 'Jealous' at New Jersey Concert

Jason Derulo joined the singer for a duet of his hit single "Want To Want Me"...and in the middle of the song, he decided to amp things up a little. Removing his pesky shirt, Derulo showed off his ripped physique as Taylor squealed in delight -- watch some fan videos of the performance below.

During the previous D.C. 1989 show, Swift brought out Lorde for an impassioned "Royals."