Most likely, the Duchess of Cambridge stayed behind to accompany Prince George, 9, Princess Charlotte, 7, and Prince Louis, 4, to their first day of school.

Following a statement from Buckingham Palace that her doctors were “concerned” for her health, the royal family flocked to Queen Elizabeth’s bedside on Thursday, but a crucial member was absent.

Kate Middleton, the Queen’s granddaughter-in-law, did not travel to Scotland with her husband Prince William to visit the Queen at Balmoral Castle for the summer. That’s probably because the three kids of the couple, Prince George, 9, Princess Charlotte, 7, and Prince Louis, 4, are starting school today. The beginning of the new school year is particularly significant for the young royals because it marks their first day of classes at Lambrook School since the family’s relocation from London to Windsor at the end of the summer.

Active mom Kate most likely remained at Adelaide Cottage for the start of the kids’ school year. But just a few weeks ago, the Duke and Duchess of Cambridge visited the 96-year-old monarch at Balmoral with their children, continuing a royal summer tradition, and Kate and the Queen got to spend some quality time together.

Kate will probably be referred to as Queen Consort when her husband ascends to the throne, but Queen Elizabeth is not known for giving out explicit “lessons,” according to insiders, so it’s unlikely that she has ever formally tutored Kate. Instead, historian Sarah Gristwood tells PEOPLE that it’s possible that the Queen treated Kate the same way she treats prime ministers in their relationship.

“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.”

Kate frequently dons jewels on loan from the monarch as a private sign of their close friendship, and she has taken her lead in dressing in bold hues to stand out in the crowd.

This summer, during the Platinum Jubilee weekend, which commemorated the Queen’s long reign, the Duchess of Cambridge served as an ambassador to Wales, took part in Trooping the Color by riding in the first carriage and joined the monarch on the balcony of Buckingham Palace to cap off the celebrations.

Prince William and Kate, both 40, “are representing the Queen impeccably,” biographer Sally Bedell Smith previously told PEOPLE. “They’re showing a kind of dedication she would be proud of. And that probably gives her hope.”