"Her Majesty Queen Elizabeth II passed yesterday, my Aunt Lilibet. She was a remarkable person who lived a remarkable life," he said.
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With hand on heart he led the attendees in a moment of silence inside the gallery in which he learned of her passing.
"She was very warm with a tremendous sense of humor and with always wise paring words," the prince recalled.
MORE: King Charles III expresses 'profound grief' after death of the queen
Price Nikolaos' cousin and godfather, King Charles III, last visited Chicago in 1986, where he was greeted by then-mayor Harold Washington and large crowds in the Loop. The then-Prince of Wales went shopping at Marshall Field's, met with students at Whitney Young High School and played polo in Oak Brook.
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"I was made an honorary citizen of Chicago in 1977, so I feel I have a great interest in what happens in this great city," he said at the time.
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"I think he's going to be an exemplary king," said Prince Nikolaos.
Prince Nikolaos' exhibition is entitled "Resilience," and features photographs exploring Greece's strong relationship with nature and environmental preservation. And it may have been the queen's resilience through decades of turmoil that defined her.
"In this somber time, it's time to reflect and celebrate all the achievements that she did, and that's what I've been trying to do, rather than being sad. I think she lived a full life," the prince said.