Queen Elizabeth II and Kate Middleton
Kate Middleton and Queen Elizabeth II during a Diamond Jubilee Nottingham visit on June 13, 2012, in England.  Getty Images/Phil Noble

Queen Elizabeth has maintained quite the poker face over the years when it comes to who she favors. When it comes to Kate Middleton, though, there's no guessing.

"The Queen is a fan," a source told Vanity Fair.

As for what makes the 93-year-old monarch an admirer, it's a trait that the two share, as well as what the Duchess of Cambridge brings to the royal family.

"Kate is unflappable," the source continued. "Her mantra is very like the Queen’s 'keep calm and carry on' approach in life, and she has the added benefit of making the Royal Family seem almost normal and in touch."

Royal biographer Claudia Joseph added that the mother of three is also a hit amongst the public, always scoring high when it comes to popularity polls.

"She’s very much the girl next door, from how she dresses to how she behaves and interacts with people on engagements," Joseph told the publication. "She is likable and relatable and that has made her very popular."

All of these traits will serve Kate well as the future Queen of England. In addition to maintaining a mindset similar to that of Queen Elizabeth, she has become a champion for different causes and taken on more royal duties.

"She has found work that she’s really passionate about," a source revealed. "She spent a lot of time at the start of her royal life learning about social issues and challenges like addiction, homelessness, mental health."

The Duchess of Sussex hasn't done it all on her own, though. An insider shared that the Queen herself had "really taken Kate under her wing," and the two "often spend hours discussing royal life and the future of the monarchy," -- that is if there is a future monarchy.

While passing the throne down the royal bloodline is the status quo, TV commentator Kevin Maguire suggested Queen Elizabeth consider the option to end the monarchy.

"... let’s get down France’s road and have a republic. It will be Great Britain," he said.