The actress stopped by The Ellen DeGeneres Show on Friday, where she recalled Prince William bestowing the damehood title on her last year, and the rather "inappropriate" noise she made after he pinned two badges on her blazer.
Reenacting the moment with Ellen DeGeneres, Thompson said, "Then he pins it right there," pointing to DeGeneres’ chest, who reacted by saying, 'Oh, God.'"
"And it’s a little bit of a nipple moment, and you go, 'Gosh, I wasn’t expecting that.' And then he pins another one underneath,” she continued,” before jokingly adding, "I'm pretty low slung these days. So, both times it hurt."
"I made very loud and inappropriate noise in Buckingham Palace. It’s not a surprise, isn’t it," she added.
"I love Prince William, I've known him since he was little, and we just sniggered at each other," Thompson shared. "I said, 'I can't kiss you, can I?' And he said, 'No, don't!'"
The 59-year-old continued, "If you're first up, you have to be more formal on such an occasion, but he's looking wonderful and doing so well. He said, 'This day isn't about me, it's about you.'"
During her time on The Ellen DeGeneres Show, Thompson also touched on how she was feeling on the eve of her 60th birthday, which is coming up on April 15.
"I’ll tell you what I think is interesting about 60," she began. "All the roles that have been imposed upon you by society since you were born, from gender roles to mom, whatever they are, start to sort of fray at the edges…And you start to think, I wonder if I was any of those things, actually, or whether I was just sort of playing along."
"I have never really asked, because I always thought it was a bit lame, but 'Who am I, actually?'" she added. "I think this decade will be fascinating."