Paloma Faith said William and Kate seemed calm when they spoke with her after she sang at the Royal Albert Hall on Thursday night, and quipped they were not bothered by her going barefoot.
It comes as the Dutch version of Endgame, penned by journalist Omid Scobie, names two members of the royal family alleged to have raised "concerns" about the skin colour of the Duke and Duchess of Sussex's son, Archie.
Scobie has been accused of being behind a "stunt to sell books" and the Dutch edition was subsequently pulled from shelves, but Kate and William did not appear to be affected on Thursday evening.
William and Kate joined other dignitaries for the Royal Variety Performance at the Albert Hall. (AP PHOTO)
After the show, Faith said: "I was just saying how relaxed they (William and Kate) are and warm. They just put you at ease, which is a skill in itself isn't it? Not everyone can do that, royal or not.
"They're good at their jobs aren't they, and it is a job."
Chinese pianist Lang Lang also performed at the show, and he claimed Kate told daughter Charlotte she would be able to play like him if she keeps practising piano.
Lang performed alongside 13-year-old Lucy, a blind and autistic girl he discovered playing on a public piano in a train station, at the Albert.
He said: "The Royal Highness was asking me about how long we were practising together, and how we discovered Lucy.
"We were talking about how we found her in Leeds Train Station, and how everything happened magically and how I'm so happy to play with her.
"We talked about Charlotte. Her Royal Highness we talked about Charlotte's piano playing, I'm sure she's good.
"Her Royal Highness said to me that she said to Princess Charlotte to say 'Hey, look, if you practice a lot you can be like him.'
"So I'm happy to be helpful a little bit. It's really funny, I was like, wow, I'm sure she will do well at the piano. I think she is practising.
He said that they discussed the acoustics in The Royal Albert Hall, and added: "I played two shows last week, it's always great to play here.
"I really love it here because they have very precise equipment, to make it sound like a smaller concert hall."
Comedian Rosie Jones said the Prince of Wales "understood" how comedy can help people with disabilities.
She said: "It was really great. It was a dream come true to meet them, and I always thought they were lovely and friendly but turns out they are.
"We were talking about comedy and about disability, and Will asked me when I started comedy and I said 'well, I've been doing comedy for as long as I remember, because having a disability means that people are awkward around me.
"I found that comedy is such a is such a great way to feel comfortable and release tension.'
She joked: "He responded really well, and he understood, so I expect him to invite me to tea - also, Dame Rosie Jones, make it happen.
"Step one, Royal Variety Performance, step two, Damehood.
"Kate was so lovely, and she said she enjoyed my performance."
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