Kate Middleton will be at the centre of more drama when she turns 40 years old and Queen Elizabeth II will look to her even more for support.

Royal biographer Katie Nicholl projected what the future holds for the Duchess of Cambridge in an interview with OK! magazine. She said the mum-of-three has over the years grown more confident and evolved into a key member of the royal household. She has proven to be a credible and reliable member of The Firm.

"Just last month, she proved how far she'd come when she hosted the royals' Christmas carol concert on her own. Standing there as a woman totally sure of herself who takes her role seriously. I think we'll see her thrive even more in her 40th year," she shared.

The author of "Kate: The Future Queen" even likened Kate Middleton to the late Princess Diana in that she too is "a fashion icon and loved by the nation." She claimed the duchess took inspiration from her mother-in-law's "work ethic and diligence" and became her own version of the "people's princess."

Nicholl also praised the royal for being steadfast and calm in the face of challenges and family drama. She believes that this year the Duchess of Cambridge will "come into her own even more" and become a strong source of support to members of the British royal family.

"Harry and Meghan's interviews this year have caused chaos for the royals, and Harry's new memoir – due out next year – will likely reveal even more intimate details about the royal family, and cause further issues. And Andrew's court case will too. Kate will step up and I know the Queen hugely values her support and will rely on her more than ever," the royal expert explained.

Nicholl also commended the Duchess of Cambridge for always sticking to the royal protocol of "never complain, never explain" even when she is the subject of criticism. Meghan Markle, in the book "Finding Freedom," allegedly complained that she felt "disappointed" by the "lack of support" from her sister-in-law. She also accused the duchess of making her cry in the leadup to her wedding to Prince Harry.

Yet throughout the drama, Kate Middleton remained silent, which is said to contribute to her popularity. Nicholl claimed the royal will only "go from strength to strength in her 40th year" and be "more cherished than ever." The duchess will, in no doubt be "at the centre of more drama" as she helps the family through a difficult year with Prince Andrew's trial and the release of Prince Harry's memoir, "but the royals know that with Kate among their ranks, they're stronger for it."

Kate Middleton
Kate Middleton, the Duchess of Cambridge will turn 40 years old on Jan. 9. Oli Scarff/POOL/AFP via Getty Images