Former U.K. Prime Minister David Cameron held practice audiences with King Charles III

The importance of King Charles shouldn't be underestimated despite the fact that the monarch in the United Kingdom is largely ceremonial, former British Prime Minister David Cameron said in an interview with "CBS Evening News" anchor and managing editor Norah O'Donnell. 

The interview comes as King Charles III takes the throne in the United Kingdom after the death of his mother, Queen Elizabeth II. The queen's funeral is scheduled to be held on Sept. 19.   

Cameron is one of 15 prime ministers who served during her 70-year reign. Just one week ago, Queen Elizabeth undertook one of her last official acts before her death: Accepting Boris Johnson's resignation and inviting incoming Prime Minister Liz Truss to form a government.