The sudden surge of followers could be attributed to the photo of Princess Charlotte's first day of school posted on the Kensington Royal Instagram account last week (see all the pictures from the memorable day here).
The photo featured the royal posing next to her brother Prince George on the steps of Kensington Palace.
"The Duke and Duchess of Cambridge are very pleased to share a photograph of Prince George and Princess Charlotte at Kensington Palace this morning. The photo was taken shortly before Their Royal Highnesses left for Thomas's Battersea. 📷 Kensington Palace," the royal family wrote in the caption.
"The recent content that has been shared, particularly Princess Charlotte's first day at school will have boosted their popularity as the trend for sharing this kind of photo among the general population shows a similarity between William and Kate's life and theirs," said Jacobs (who is Head of Ads at marketing agency Distract).
"If you get into the details, there are as many as four times more likes for those photos than ones simply depicting the couple's royal duties.
"The trick here is not to overshare, they have the right idea when it comes to selective content."