Never before have we wondered if King Charles III has seen “The Vampire Diaries,” but after watching him make small talk with Nina Dobrev, the concept is now front of mind. The king himself was the man of the hour, alongside Queen Camilla, at the fifth annual King’s Trust Gala, held Wednesday at Christie’s in Midtown Manhattan. Marking 50 years of the charity, which was called the Prince’s Trust until 2024, this year’s benefit featured an appearance by the royals, which was Charles’ first trip to New York since 2007. The gala began with a 4:30 p.m. red carpet and cocktail hour, where trays of “the queen’s cocktail” were on offer (gin, bitters, elderflower liquor and vermouth with a twist). Ralph Lauren , along with Ricky and David, were early arrivals, chatting with the CFDA’s Steven Kolb.…