Kate Middleton Is Embracing Change Ahead of 40th Birthday: 'She Has Come Into Her Own'

The mom of three is "flourishing" as her milestone birthday approaches, says a royal insider

Kate Middleton.

Kate Middleton is approaching a milestone birthday — and a new chapter in her royal and personal life.

The Duchess of Cambridge, who will turn 40 on January 9, is "flourishing," a royal insider tells PEOPLE in this week's cover story. "She has really come into her own."

Kate is preparing more than ever for her role as future queen consort alongside husband Prince William, taking on more royal duties as Queen Elizabeth has canceled engagements due to recent health issues as well as Prince Harry and Meghan Markle's decision to step back as senior working royals.

Most recently, Kate hosted her first-ever Christmas carol concert at Westminster Abbey in tribute to the incredible work of individuals and organizations across the U.K. who have supported their communities through the COVID-19 pandemic.

Kate Middleton. Pool/Max Mumby/Getty

In the program for the concert, Kate wrote, "Through our separation from others, we have been reminded just how powerful human connection is to us all. Just how much we need one another. And how loving and feeling a sense of belonging to one another can provide comfort in tough times. The importance of simply being together."

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Joan Black, who attended the concert in recognition of her work helping the elderly during the lockdowns, tells PEOPLE: "What she wrote was beautiful, and to bring everyone together like this is lovely. I felt she was really confident. We are doing well if that's our future Queen."

The Cambridge family's 2021 Christmas card. Duke and Duchess of Cambridge/Instagram

Kate has also entered into a new family dynamic. With 3-year-old son Prince Louis off to nursery school, all three of the couple's children are out of the toddler years. Still, Kate is heavily involved in the lives of Prince George, 8, Princess Charlotte, 6, and Prince Louis despite the helpful hand of nanny Maria Turrion Borrallo.

Kate "runs things at home with the kids and the schedules," says a friend. "She is hugely involved in every single part of their day."

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Kate is "more and more impressive as time goes on," says a source close to the royal household. "She is a focused and professional woman."