Ruby announced her mother's passing Tuesday night ... calling her a hero and "Mother of the Civil Rights Movement." Lucille's cause of death is unknown but Ruby paid a touching tribute to her saying, "Today our country lost a hero. Brave, progressive, a champion for change. She helped alter the course of so many lives by setting me out on my path as a six year old little girl."

Lucille -- who gave birth to Ruby the same year as the landmark decision of Brown vs. Board of Education to end racial segregation in schools -- is memorialized alongside Ruby in Norman Rockwell's famous painting, "The Problem We All Live With" ... which shows Ruby carrying her school supplies as U.S. Marshals escort her.

When the NCAAP requested Ruby attend the all-white William Frantz Elementary School as a first-grader in 1960 ... Ruby's father, Abon Bridges, was reluctant. But, according to the National Women's History Museum, it was Lucille who insisted because she wanted Ruby to have the education she herself missed out on. Lucille walked Ruby to school every day amid hateful and racist rhetoric spewed in their direction.

New Orleans Mayor LaToya Cantrell said, "Lucille's strength was unbounded during this period. Lucille insisted, seeing the action as an opportunity to help all Black children, and walked Ruby, with federal marshals, past chanting and taunting white protesters and to the schoolhouse. Mother and daughter both revealed their character and courage."

Rockwell's painting came back into the spotlight during the run-up of the presidential election ... with an adapted version showing now Vice President-elect Kamala Harris walking with Ruby's shadow cast on a white wall. The painting's been dubbed "That Little Girl Was Me."

Ruby wholeheartedly approved the image saying, "I am Honored to be a part of this path and Grateful to stand alongside you, Together with Our fellow Americans, as we step into this Next Chapter of American History!"

Lucille had 5 children. Her husband died in 1978.

She was 86.