Eartha Kitt's Amazing Journey From Abandoned and Abused to Hollywood Legend: New Book

"There were two different people that coexisted within my mother," Kitt Shapiro tells PEOPLE. "One was Eartha Kitt. The other was Eartha Mae. They were two distinctive parts that made one person."

Eartha Kitt was the legendary entertainer who seduced audiences worldwide and whose signature purr as Catwoman in the late '60s made the role all her own. Eartha Mae was born into poverty in the small town of North, South Carolina, the illegitimate daughter of a young Black woman and a man she assumed to be white — and whose identity she never knew.

"Eartha Mae was the one who gave her strength," says Shapiro, who's new memoir Eartha & Kitt: A Daughter's Love Story in Black & White, is excerpted in this week's PEOPLE. "My mother would often say, 'I've used all the manure that's been thrown on me as fertilizer.'"

"But she also overcame," she adds.

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Even when she urged her mother to let go of her childhood pain, her response was always the same: "Why would I let it go?" she'd say. "It's who I am and it made me who I am."

Eartha Kitt's mother, Anna Mae Keith, "was only 16 and married when my mother was born," writes Shapiro. "My mother always assumed that she was probably conceived by rape... it was assumed he had been white."

Both illegitimate and of mixed race, Eartha "was treated as an outcast," she writes. When her mother met a man who offered to marry her, he demanded that she leave Eartha behind, telling her "I don't want that yella gal in my house."

"At the time in the South they referred to her as a 'yella gal,' because she was mixed race," says Shapiro.

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And so, at the age of five or six, Eartha was sent to live with another family where she cleaned house, picked cotton in the fields and was mocked and beaten. Eventually an aunt in Harlem sent for her and she arrived by train, wearing the few pieces of clothing she owned because she did not have a suitcase.

After her talent for singing and dancing was noticed by a school teacher, she received a scholarship to a prestigious Black dance company and began touring Europe. One night in Paris, she was asked to perform solo. With no act and no costume to speak of (she ran out and bought a bolt of cloth to make a dress), she said yes.

Over the next six decades, she sang all over the world. And at her side was her daughter Kitt. "She named me Kitt because she wanted to be sure that her name lived on," says Shapiro.

The only daughter of Eartha and her husband Bill McDonald, she was raised by her mom. (McDonald became addicted to opioids after suffering severe injuries from a grenade explosion in the Korean War. His addiction, plus her mother's constant traveling, eventually led to their divorce in 1964.)

For more from Eartha & Kitt, pick up this week's issue of PEOPLE, on newsstands Friday.

Theo Wargo/Wireimage

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"She was a fierce protector of me," says Shapiro. "We were a team."

Throughout her life, Shapiro witnessed how her mother always spoke up for those who could not. Whether against the Vietnam War, a stance which almost cost her her career and launched an unwarranted investigation by the CIA, or in support of civil rights, she notes, "She used her voice to defend people who didn't have voices."

"She never understood why people should be pigeonholed by race, religion, and sexual orientation," says Shapiro.. "Her point was we're all human beings. We're all part of the human race. The worlds a global place in which we're all connected."

Together till the end, she writes how her mother died in her arms on Christmas Day in 2008 from colon cancer at age 81. How fitting that the woman known for her sultry rendition of "Santa Baby," a song that was written for her, died on Dec. 25. "She knew the importance of timing," says Shapiro with a laugh, "and in a way, it was poetic."

Shapiro, 59, who owns a clothing boutique in Westport, Conn. and oversees her mother's estate, now works with American Cancer Society and Colon Cancer Alliance to increase awareness about the importance of screening and early diagnosis.

She hopes her mother's story will inspire others. "My mother survived so much," says Shapiro. "She was a single woman of color who made a name for herself by sticking to who she was, following her heart, and being her own person. She was a woman of incredible strength."

Shapiro's book Earth & Kitt is out May 4.