The Fashion designer - who chose the 37-year-old supermodel to close his Louis Vuitton runway show in February - believes the British beauty's enduring appeal is her "huge" presence and energy, and believes there are very few people like her.
He told America's Vogue magazine: "I mean Kate is, besides being physically beautiful and an incredibly charismatic and extraordinary personality, just very rare - if not totally unique.
"Kate can be just Kate, and the presence is just huge. She fills space, indoor and outdoor, studio space and pages, with such life. That energy really comes through in any and everything that she does."
Marc was among the guests at Kate's wedding to Jamie Hince last month and he says the nuptials were "beautiful".
He told America's Vogue magazine: "It was this beautiful, spontaneous moment. It was so seamless."
Meanwhile, photographer Mario Sorrenti - a former boyfriend of Kate - has praised the "well dressed" guests at the wedding.
He said: "It was incredible. It was so well done, and everybody was like so elegant, so well dressed."