Eugénie de Danglars
Eugénie de Danglars, usually referred to as Eugenie, is the childhood friend of Albert de Morcerf and Franz d'Epinay who is engaged to Albert. The three were close and went everywhere together; sometime after the engagement, she was left out / drifted out of the company, and points this out to Albert. Though she is usually friendly to him, she appears displeased with the arrangement and is seen to repay his foolishness with scorn, warmth with coolness, and complaints with disdain.
We first catch this falling out at the height of her realization of what is lacking, and the very beginning of when Albert is developing an inkling that there might be something wrong, so as he wrestles with the problem, Albert's good nature of course swings the balance the other way: Eugenie responding to him as she realizes he cares. Later in the series, she shows some feelings towards Albert and she soon realizes that she has fallen in love with him, even sharing a kiss with him.
She shows her affections through composing music for and playing the piano; her dream is to become a professional pianist. With Albert's help, she escapes her wedding and departs Paris for New York City, both to escape her father and arranged marriage and to study music at a prestigious conservatory. During the epilogue set five years later, she has become a world-renowned pianist and has returned to Paris, where she is reunited with Albert.