Prince Charles and the Duchess of Cornwall have certainly packed a punch while on their tour of the US, cramming in plenty of sights during their four-day visit and attracting visitors from far and wide. And the final day of their tour saw the couple receive a warm message from boxing royalty. Boxing legend Muhammad Ali paid tribute to the Prince as he and Camilla arrived in his home city of Louisville - describing the heir to the throne as 'the greatest'. Scroll down for the video . The final leg: Prince Charles, wearing a light blue suit, gingerly walks down the aircraft steps after landing on the tarmac in Louisville, Kentucky. The Duchess of Cornwall follows closely behind . Flying high! The standard for the Prince of Wales and the United States flag are flown from the cockpit of the plane carrying Prince Charles and Camilla as it lands in Louisville . Welcome to Kentucky! The Prince of Wales is greeted by by the Governor and First Lady of Kentucky, Steve and Jane Beshear after touching down at Louisville International Airport . The sport star's words came in a letter - not in person - as he was not well enough to join leading figures from the city at a cultural greeting for Charles and Camilla. But the presence of the three-time former world heavyweight boxing champion was still felt when a letter written by him was read to the prince. The 73-year-old sports star, considered by many to be the greatest boxer of all time, retired in 1981 and has suffered with Parkinson's disease since the mid-1980s. A marching band greets the royal couple as they arrive at the Kentucky Center for African American Heritage . The pensive Prince: Charles interacts with exhibitors while touring a cultural festival at the Kentucky Center for African American Heritage . Although boxing legend Muhammad Ali (pictured here in 2014) was too ill to attend, he did send a heartfelt letter welcoming Charles and Camilla to his home city of Louisville . Clap along! Charles and Camilla burst into applause following a presentation by local residents in Louisville . Superfan: Renate Elmore of Louisville, complete with Union Jack hat and bag, waited outside the gates of the Kentucky Center for African American Heritage in order to try and catch a glimpse of Charles and Camilla . Meet me in Louisville! Prince Charles meets local dignitaries in front of the iconic Big Four Bridge . The royal couple were visiting the Kentucky Centre for African American Heritage - a stone's throw from Ali's childhood home - Louisville's Mayor Greg Fischer welcomed the royal couple. The welcome was, on every level, a traditional one. A choir serenaded with a rendition of 'My Old Kentucky Home' and later the couple toured stands showcasing the state of Kentucky and Louisville's heritage, culture, history and sustainability projects. Mr Fischer reading Ali's words said: '(My wife) Lonnie and I welcome you to our hometown of Louisville, Kentucky, USA. We are honoured that you have come to explore, share and learn about new sustainable initiatives that are so close to your heart.' The former sportsman could not help mentioning the state's successful college basketball team which is on a long winning streak. Ali added: 'Louisville prides itself on being a compassionate city and we are confident that you will leave feeling a sense of our southern hospitality, caring for the environment, and yes - our love for college basketball. '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. 'We think you are the greatest.' Life down on the farm: Charles and Camilla visit a Food Literacy Project at Oxmoor Farm, Louisville . All ears: Camilla leans in as a staff member at Neighborhood House, a community outreach centre in Louisville's West End neighbourhood explains the centre's story . The Duchess speaks with a group of teenagers while visiting Neighborhood House, a community outreach center in Louisville's West End neighbourhood . Grandmother in waiting! Camilla chats to local children at Neighborhood House and, right, joins a toddler and baby group . Their trip has been full of sporting moments. Yesterday, the Prince of Wales went bowling at the Armed Forces Retirement Home in Washington D.C and managed to knock over four pins - much to the delight of veterans and a watching Duchess of Cornwall. Along with a visit to the bowling alley, the royal couple were also shown the library, which boasts stunning views of the Washington Monument, and the wellness facilities for the pensioners who live there. The couple also took time on their final day to visit the Food Literacy Project at Oxmoor Farm in Louisville where Camilla found herself making pizzas with a group of youngsters who insisted on topping it with carrots and radishes. Camilla joined children from Louisville, Kentucky who were part of a 'from field to fork' group learning not only how to grow their produce but cook it. After helping the youngsters plant a rhubarb plant in a plot at Oxmoor Farm, an 18th century estate, she sat around a table in the open air and helped nine-year-old Fred Meadows create the savoury treat. The children use seasonal produce in their cooking so radishes, kale and carrots were added to the pizza - but they were cooked after the Duchess had left the group. Earlier the Duchess had visited a community project called Neighbourhood House, running since 1896 in a disadvantaged area of Louisville. Originally rich members of the community moved into the neighbourhood, with affluent and poor members living together and raising standards. She chatted to Jason Logsdon, 11, who comes to the centre every day to do homework or sport and he told the Duchess he wanted to join the CIA when he is older. He said: "I knew who she was but not much about her, but she was awesome, she's cool." The Duchess ended her visit to Louisville by visiting the home of the world famous Kentucky Derby - the Churchill Downs racecourse - to celebrate the work of the Brooke. Camilla is president of the Brooke a worldwide equine welfare charity and her visit marked the official launch of its American fundraising branch. She also met a pair of donkeys and gave them treats and chatted to jockeys and their mounts. Other highlights from the day included hearing an employee for local spirits maker Brown-Forman Corp. showing how bourbon barrels are made. There was also a brief stop at one of the city's most recognisable landmarks, the Big Four Bridge.
The final day of their four-day visit to the US takes in Louisville, Kentucky . A welcome letter from  boxing legend Ali is read out to the royal couple . The couple visited the Kentucky Centre for African American Heritage . Charles and Camilla chatted with teens at the Food Literacy Project at Oxmoor Farm in Louisville .