During a whirlwind visit to Louisville yesterday, Charles chatted with onlookers, attended panel discussions and called for fundamental changes toward a more sustainable economy in sync with the environment.
"If we wish to maintain our civilisation, then we must look after the Earth," Charles said in a speech at the Cathedral of the Assumption. "In failing Earth, we are failing humanity."
"As a grandpa, I have no intention of failing mine or anyone else's grandchildren," he said.
Charles and his wife, Camilla, were serenaded by a choir singing "My Old Kentucky Home" at the start of their visit.
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They received a welcome from the city's most famous native son boxing great Muhammad Ali that was read by the city's mayor.
"As you travel back to your homeland, we hope you know how much this city respects and admires the many contributions you have made in the world," Ali wrote in the message read by Mayor Greg Fischer. "We think you are the greatest."
"He had a lot of questions about what the oak does to the product, and what creates the ... Flavors that we have with our products," said the employee, Chad Ruch.
Schoolchildren lined up outside the royal couple's event at the Kentucky Center for African American Heritage. Charles and Camilla shook hands and chatted with some of the youngsters.
Jailen Leavell, 15, was part of the River City Drum Corps that played for Charles and Camilla.
"This morning I just could not sleep," the teenager said. "I woke up at 4 o'clock just thinking how in the world was I going to handle this. Being able to actually see him is very surreal."
The Kentucky stop concluded the royal couple's visit to the US, which included a visit to Washington, DC.