Princess no Kakurega

Lizzy has taken second place to her beautiful sister, Maria, for too long. One day, Maria dies in a traffic accident and Lizzy decides to adopt her sister's orphaned son, Ben, whose father is unknown. Since then, she has been living a happy life as a single mother. But one day Prince Enrico comes to claim Ben, saying his deceased brother is Ben's father. Ben is the only heir to the throne of his principality. "I have nothing to live for but Ben!" Lizzy firmly refuses Prince Enrico's claim....

(Source: fictiondb)