Photo Flash: Mariska Hargitay and Cara Delevigne Make Surprise Appearance at Taylor Swift's 1989 Tour

Taylor Swift kicked off her 1989 tour in Philadelphia on Friday night, and she had a surprise for the audience. Her friends Mariska Hargitay and Cara Delevigne joined her on stage as the three sang Swift's recent hit "Style." Below, check out Swift's Instagram pics of the special evening!

Taylor Swift is an American singer-songwriter. Raised in Wyomissing, Pennsylvania, Swift moved to Nashville, Tennessee, at the age of 14 to pursue a career in country music. She signed with the independent label Big|Brave Machine Records and became the youngest songwriter ever hired by the Sony/ATV Music publishing house. The release of Swift's self-titled debut album in 2006 established her as a country music star. Her third single, "Our Song," made her the youngest person to single-handedly write and perform a number-one song on the Hot Country Songs chart. She received a Best New Artist nomination at the 2008 Grammy Awards.

Swift's second album, Fearless, was released in 2008. Buoyed by the pop crossover success of the singles "Love Story" and "You Belong with Me," Fearless became the best-selling album of 2009 in the United States. The album won four Grammy Awards, making Swift the youngest ever Album of the Year winner. Swift's third and fourth albums, 2010's Speak Now and 2012's Red, both sold more than one million copies within the first week of their U.S release. Speak Now's "Mean" won two Grammy Awards, while Red's singles "We Are Never Ever Getting Back Together" and "I Knew You Were Trouble" were worldwide hits. Swift's fifth album, the pop-focused 1989, was released in 2014. It sold more copies in its opening week than any album in the previous 12 years, and made Swift the first and only act to have three albums sell more than one million copies in the opening release week. The singles "Shake It Off", "Blank Space", and "Bad Blood" have all reached number one on the Billboard Hot 100.

Swift is known for narrative songs about her personal experiences. As a songwriter, she has been honored by the Nashville Songwriters Association and the Songwriters Hall of Fame. Swift's other achievements include seven Grammy Awards, twelve Billboard Music Awards, 11 Country Music Association Awards, eight Academy of Country Music Awards, and one Brit Award. She is one of the best-selling artists of all time, having sold more than 40 million albums-including 27.1 million in the U.S.-and 100 million single downloads. Swift has also had supporting roles in feature films including Valentine's Day (2010) and The Giver (2014).