Taylor Swift was joined on stage by Fall Out Boy lead singer Patrick Stump for her 'Red' tour show in New Jersey last night (13th July).
The artists performed 'My Songs Know What You Did In The Dark (Light Em Up)' in front of 55,000 fans at the MetLife Stadium in East Rutherford.
The track is taken from Fall Out Boy's latest album 'Save Rock And Roll' and previously got strong words of praise from Taylor when it was first released.
Her 'Red' tour has also seen special guests in the form of Nelly and Train's Pat Monahan join her at various dates.
Earlier this year, the country star was also a surprise guest herself when she joined the Rolling Stones for a performance ahead of her set at Capital FM's Summertime Ball 2013.
Meanwhile, the singer is among the stars from the music world reacting to the news that Glee star Cory Monteith was found dead in his hotel room yesterday.
The pair performed 'My Songs Know What You Did In The Dark (Light Em Up)' together on stage last night.