Kate Middleton and Prince Williams always get to meet several celebrities during their engagements. But, in one recent event, the Duchess of Cambridge revealed how "upset" their kids were upon learning that their parents would meet a celebrity that they admire the most.

The revelation came after the trailer for the Duke of Cambridge's upcoming ITV documentary emerged earlier this week, according to OK! magazine. In Prince William: A Planet For Us All, the royal couple met with Sir David Attenborough, where they discussed the "growing environmental" concerns in the world today.

Upon walking towards the famous environmentalist, the Duchess shared her greetings. Following her husband's introductions, Kate Middleton said that their children were "very upset" as they were not coming with them to meet the celebrity.

She continued that the young royals, particularly Prince George and Princess Charlotte, are "massive fans" of Sir David Attenborough. This seemingly delighted the 94-year-old "legend" and TV veteran as he visited Kensington Palace to meet the kids on Thursday.

Several photographs of the warm engagement inside the palace went public after. Kate Middleton and Prince William, also, posted a few snaps on their official social media accounts, marking the first meeting of Queen Elizabeth's friend and the young Cambridges.

The Daily Mail reported that the photos were taken after the naturalist enjoyed a "private viewing" of Life On Our Planet with the Duke of Cambridge. This, also, marks an important engagement ahead of the royal-born Prince's upcoming documentary, Prince William: A Planet For Us All, which features the naturalist.

Following the meeting, Sir David Attenborough revealed his thoughts to The Times about the young royals. He said that he found Prince George, Princess Charlotte, and Prince Louis "charming," adding that it was a "nice domestic occasion."

Aside from meeting them, he, also, gave Kate Middleton's eldest son a fossilized tooth of a giant shark. Reports said that the television personality found it during a family holiday in Malta in the late 60s.

He, later on, recalled that when he was young, a grown-up did the same thing toward him, which got him thinking to do the same for the young Cambridges. Attenborough, then, shared how "interested" Prince George and Princess Charlotte are when he gave the fossil.

During their engagement inside Kensington Palace, all of the Cambridges, alongside Sir David Attenborough, practiced social distancing measures. Even during their screen time, they arranged the chairs with enough spacing to follow the safety protocols.