"Catherine has learned by observing," the Queen's biographer Sally Bedell Smith tells PEOPLE in this week's cover story. "She knows what resonates. She will have absorbed a lot from this Queen."
Although they are separated in age by 56 years, the Queen and Kate share key qualifications for the job: quiet stoicism, unerring discretion and firm loyalty. Their opinions on contentious political issues are never heard; their commitment to the throne is unwavering, and their public images are tightly controlled. Kate also embodies the Queen's unofficial motto for public life: "Never complain, never explain."
Not one to hand down explicit "lessons," it's unlikely the Queen has ever formally tutored Kate, insiders say. Instead, historian Sarah Gristwood tells PEOPLE that the Queen may have approached her relationship with Kate the way she does with prime ministers.
"The Queen has always preferred to do rather than to say," says the author of Elizabeth: Queen and Crown. "With her audiences with her prime ministers, if there has been actual advice, it would be a discreet 'I think that went rather well' rather than actual instruction."
Samir Hussein/WireImage Queen Elizabeth and Kate Middleton in 2019
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Kate is also a modern woman who is nonetheless amenable to the centuries-old power structure of the family business — otherwise known as the "the firm."
"It's a personal willingness to conform to the requirements of the institution," says Gristwood. "That sounds like an unappealing, unglamorous virtue, but it's an important one if you're going to be a successful cog in the royal wheel."
Kate has even been inspired by the Queen's style and regularly wears jewels on loan from the monarch. On royal outings, the Queen always wears bright colors so fans can spot her in a crowd — and Kate has followed suit.
The Queen "has this definitive style, almost like a uniform, which also works for Kate," a friend tells PEOPLE.
Samir Hussein/WireImage Prince William, Kate Middleton, Prince George, Princess Charlotte and Prince Louis joined Queen Elizabeth and Prince Charles on the Buckingham Palace balcony on June 5.
As the Queen begins her summer holiday at Balmoral Castle in Scotland this week — two months after her 70 years on the throne was celebrated across the U.K. and the world — she's doing so with confidence in the fact that Kate and her husband Prince William are ready for their royal duties in the months and years ahead.
They "are representing the Queen impeccably," adds Bedell Smith. "They're showing a kind of dedication she would be proud of. And that probably gives her hope."