King Charles secret strength - Kate Middleton or Prince William?

King Charles III is said to be very much inspired of his beloved daughter-in-law Kate Middleton's steadfastness with the Firm and the royal family.

Prince William and Princess Kate are an "incredible enhancement" to the King and Queen Camilla," according to royal biographer Sally Bedell Smith. 

“She knows the important role the family plays in building relationships globally on behalf of the U.K,” a royal source told PEOPLE. 

"It is clear that she and the King are quite close — in some respects closer to him than William," added the insider.

The insider went on claiming: "Kate has acted as the honest broker" during William and Harry’s "fractious relationship" with their father.

Princess Kate has proved to be real gem of royal family with her loyalty to King Charles and her husband Prince William: "She has this public image of being nice and smiley and, dare I say, innocuous. But she is actually strong-minded, strong-willed and prepared to fight for what she wants and what she thinks is right," royal author Valentine Low told the same media outlet.

Some royal fans and expert believe that King Charles will never let Kate feel lost in ongoing rift with Prince Harry's wife Meghan Markle.