Boxing legend Muhammad Ali welcomed the Prince of Wales and Duchess of Cornwall to his home city of Louisville, describing Charles as "the greatest".
The sport star's words came in a letter rather than in person as he was not well enough to join leading figures from the city at a cultural greeting for the royal couple, who were in the city on the final day of their US tour.
The Prince of Wales said during his acceptance speech that he realised he had been coming to the US for the past 40 years.
"Look what it's done to me," he joked before saying his only anxiety about the evening was "that I might quite possibly send my wife to sleep during my speech."
Barack Obama told Prince Charles that American people rate UK royalty above their own politicians on the royal couple's Washington tour.
Watch Prince Charles try - and fail - to get a strike on the bowling alley during a trip to a veterans' retirement home in Washington.
Charles and Camilla spent a busy first full day of their US trip visiting memorials to President Abraham Lincoln and Martin Luther King Jnr.