Promise at Dawn (1971)

Nina is a former silent-film star from Russia who abandons her career to care for her son. She is a single mother -- the boy's father is a famous actor who wants nothing to do with either Nina or her child. She joins an acting troupe where she impersonates a famous French fashion designer, but she leaves the group in Krakow, Poland, when her true identity is discovered. She travels to France, taking several odd jobs in Nice to support her son. When the boy grows to young adulthood, he is recruited to fight during World War II for the French and later the British. He is decorated for valor and returns to locate his estranged mother after two years have passed. Upon arriving home, he finds that his mother had died several years earlier but that she meticulously wrote over 250 letters to give her son moral support and encouragement in the years to come.