Sir David, 94, brought the tooth with him as he met William, Kate, both 38, Prince George, seven, Princess Charlotte, five, and Louis, two, at the palace of Kensington.
He attended a private screening of his new environmental documentary with the Duke of Cambridge – which took place in Palace grounds.
William and the seasoned broadcaster watched A Life On Our Planet, a revealing and powerful first-hand tale in which Sir David reflects both the defining moments in his life as a naturalist and the devastating changes he has witnessed.
Socially distanced in the open air, The Duke of Cambridge and Sir David were offered director chairs with their names printed on the back – but in a change of plan, they sat inside each other.
The 94-year-old broadcaster chatted with William, Kate and their three children George, Princess Charlotte and Prince Louis after Thursday’s screening.
Famous clips from the documentary include him rolling with baby gorillas in Rwanda, The Sun reports.
William interviewed Sir David at the World Economic Forum in Davos, Switzerland, last year, and during the discussion, the broadcaster warned that humanity must act not to “wipe out part of the natural world”.
With a shared passion for protecting the natural world, humans continue to support each other in their mission to address some of the greatest environmental challenges facing the planet.
This includes collaboration on the William’s Earthshot Prize, an ambitious global environmental project announced last December to tackle climate issues.
Further pricing details are expected in the coming weeks.
The giant shark tooth given to George was discovered by Sir David during a family vacation in Malta in the late 1960s.
It was embedded in the soft yellow limestone of the island, which was laid during the Miocene period around 23 million years ago.
The Carcharocles megalodon is believed to have grown to 15 meters in length, about twice the length of the great white shark.
David Attenborough: A Life On Our Planet, produced by WWF and Silverback Films, hits theaters Monday and premieres on Netflix on October 4.
An accompanying book is published on October 1.
Sir David joined Instagram this week, reaching over a million subscribers in just a few hours.