If Fanny and Felix Mendelssohn had lived and launched musical careers a century later, they would have received top star billing as a brother-sister duo. But since the sibling child prodigies were creatures of their times, Felix's star shot up like a comet while Fanny, so to speak, had her "15-minutes of fame". Her father's dictum held for the rest of her life: "Perhaps music will be his [Felix’s] profession, whereas for you it can and must be but an ornament...."

Fanny Mendelssohn was born in Hamburg, the eldest of four children born to a wealthy banking Jewish family that converted to Protestantism in 1922, a move that freed them from the scourge of anti-Semitism in 19th century Europe and guaranteed their assimilation into the cultural life of the German upper class. The family also adopted the name Bartholdy. Felix, the second child, was born four years later. Both received their first music lessons from their mother, who taught piano. But the musical talent of both children was evident very early in their childhoods, and so their parents, who gave great currency to learning and culture, gave them the best musical and general education money could buy - in Berlin and Paris where the family maintained homes and businesses. In Paris, they took piano lessons from Marie Bigot who was a friend of Beethoven; in Berlin, they learned composition from the German composer Carl F. Zelter who was then director of Berlin's famous Singakademie, received piano lessons from the renowned virtuoso Ludwig Berger, while the philosopher Karl Hayse supervised their general education. The two child prodigies were not surprisingly devoted to each other and remained so throughout their lives.

Fanny excelled in composition and showed great talent for performance as well, and her skills clearly outshone everyone else's, including Felix's. At 13 years, she could play from memory all 24 of Bach's "Well-tempered Klavier" (Book 1), and at 14 she gave as a birthday gift to her father her first composition, a song she called "Songs, fly joyously away!" More compositions soon followed: 38 songs, 11 piano pieces, 4 choral arrangements, a chorus and various arias.

Clearly she was meant for a life in music and music did remain very much at the center of her life even after her marriage to the painter Wilhelm Hensel. She continued to write music - about 500 largely unpublished works have survived, some large-scale works, mostly lieder and pieces for piano written in her own hand. Her music received an audience in her lifetime, but not from center stage of Europe's famous concert halls - that was Felix's good fortune. Instead she did the next best thing and brought the concerts to her home, reviving the Sunday morning musical salon that her mother had held before her. At her Sonntagmusik concerts which were fairly large events attended by eminent musicians and the intellectual elite, Fanny conducted the orchestra and chorus and performed her own works. The concerts gained for her and works a degree of recognition, but just as her musical life was finally getting the lift it deserved, fate intervened. Felled by a stroke on a day of rehearsal for one of her Sunday concerts, she died that same evening - on May 14, 1847. And in a curious twist of fate, Felix, whose career had prospered beyond dreams, died a few months later on November 4.