Tina Knowles has spoken.

Though Beyoncé and Solange’s mom sits at the center of arguably the most famous, and famously private, families in the world, living her best life means using her voice.

Initially, “I didn’t want to write a book because I thought [people] only want to know all my kids’ business. They’re not going to be interested in me.” Knowles, 71, tells PEOPLE in this week’s World’s Most Beautiful issue of penning new memoir Matriarch. “I’ve lived this incredible life, and you really don’t realize it until you start writing everything down.” 

Her writing journey actually began long ago. “I started, probably about 12 years ago, just recording my story, which I think everyone should do, for my great grandchildren, because for some reason, I just started thinking about the fact that I never met my grandparents and the history that I gathered for my mom,” she says of her late mother Agnes Buyincé (their surnames differ due to a hospital clerical error when Knowles was born).

“I wish that I would have asked her more. I wish I would have investigated more.”

Originally, “it wasn’t supposed to be a memoir. I was going to do a behind-the-scenes type thing with Destiny’s Child and just with the entertainment industry,” she explains.

“And when I started telling the story and listening back to what I had recorded, I was like, it’s time to do a memoir, because I want to leave that legacy for my kids. But I also want to encourage young people and older people to go and record their parents and get those stories.”

That said, Knowles didn’t originally plan to discuss her difficult first marriage and divorce or even her breast cancer diagnosis in the book. “It was very carefully written at first,” she says. “But then it was like, this doesn’t even make sense because there’s only all the positive stuff. And there was a lot of positivity, you know, but, no, I didn’t plan on writing that.”

She admits that with her famous kids and rumors that come up about their family, “I’m told all the time that I have to be quiet, and it’s not like I like speaking out, but sometimes I just do have to speak out — I do, because it just gets to be too much.”

But with this book, she says, “It’s my story. Everything that happened in my life has happened to bring me to this point. Probably the most painful parts of my writing were the losses of my mother, my father, of my [cousin] Johnny, of Solange’s best friend. The deaths were the hardest part, and I cannot get through them without crying.”

“It’s been a rollercoaster,” Knowles says of her incredible journey, “but it’s been amazing, an amazing ride. I wouldn’t trade it for anything in the world.”

Matriarch is available now wherever books are sold.

For more on Tina Knowles’ life and loves, pick up this week’s issue of PEOPLE, available on newsstands everywhere now.