Former US secretary of state Condoleezza Rice and Aretha Franklin took the stage in a rare duet for Rice, the classically trained pianist, and Franklin, the soulful voice of a generation.
Their aim was to raise money for urban children and awareness for music and the arts.
"It is a joint effort for the inner-city youth of Philadelphia and Detroit," Franklin said before their concert with the Philadelphia Orchestra in the city's Mann Music Centre.
Their appearance in the three-hour concert before an estimated crowd of 8,000 overflowed with Franklin's catalogue of hits and arias from the world of opera and classical music.
"We decided to give it a try," Franklin said. "So here we are, in the city of Brotherly - and Sisterly - Love."
Rice, better known as a diplomat and national security adviser, accompanied Franklin singing her hit I Say A Little Prayer as well as My Country 'Tis of Thee.
Rice said she rehearsed furiously for her performance of Mozart's Piano Concerto in D Minor with the orchestra.
Franklin's repertoire included songs from her new album A Woman Falling Out of Love, to be released later this year.